RAC USEFUL DOCS, SCRIPTS AND COMMANDS

Oracle RAC Load balancing and Failover
LOAD BALANCING in RAC:-
The Oracle RAC system can distribute the load over many nodes this feature called as load balancing.

There are two methods of load balancing
1.Client load balancing
2.Server load balancing

1.Client Load Balancing
Client Load Balancing distributes new connections among Oracle RAC nodes so that no one server is overloaded with connection requests and it is

configured at net service name level by providing multiple descriptions in a description list or multiple addresses in an address list. For example,

if connection fails over to another node in case of failure, the client load balancing ensures that the redirected connections are distributed among

the other nodes in the RAC.

Configure Client-side connect-time load balancing by setting LOAD_BALANCE=ON in the corresponding client side TNS entry.

TESTRAC =
(DESCRIPTION =
(ADDRESS_LIST=
(LOAD_BALANCE = ON)
(ADDRESS = (PROTOCOL = TCP)(HOST = TESTRAC1-VIP)(PORT = 1521))
(ADDRESS = (PROTOCOL = TCP)(HOST = TESTRAC2-VIP)(PORT = 1521))
)
(CONNECT_DATA = (SERVICE_NAME = testdb.selectstarfrom.com))
)

2.Server Load Balancing
Server Load Balancing distributes processing workload among Oracle RAC nodes. It divides the connection load evenly between all available listeners

and distributes new user session connection requests to the least loaded listener(s) based on the total number of sessions which are already

connected. Each listener communicates with the other listener(s) via each database instance’s PMON process.

Configure Server-side connect-time load balancing feature by setting REMOTE_LISTENERS initialization parameter of each instance to a TNS name that

describes list of all available listeners.

TESTRAC_LISTENERS =
(DESCRIPTION =
(ADDRESS_LIST =(ADDRESS = (PROTOCOL = TCP)(HOST = TESTRAC1)(PORT = 1521)))
(ADDRESS_LIST =(ADDRESS = (PROTOCOL = TCP)(HOST = TESTRAC2)(PORT = 1521))))
)

Set *.remote_listener= TESTRAC_LISTENERS’ initialization parameter in the database’s shared SPFILE and add TESTRAC_LISTENERS’ entry to the

TNSNAMES.ORA file in the Oracle Home of each node in the cluster.

Once you configure Server-side connect-time load balancing, each database’s PMON process will automatically register the database with the database’s

local listener as well as cross-register the database with the listeners on all other nodes in the cluster. Now the nodes themselves decide which

node is least busy, and then will connect the client to that node.

-----------------------------------------------------------------------------------------------------------------------------------------------------

--------

FAILOVER in RAC:-
The Oracle RAC system can protect against failures caused by O/S or server crashes or hardware failures. When a node failure occurs in RAC system,

the connection attempts can fail over to other surviving nodes in the cluster this feature called as Failover.

There are two methods of failover
1. Connection Failover
2. Transparent Application Failover (TAF)

1. Connection Failover
If a connection failure occurs at connect time, the application failover the connection to another active node in the cluster. This feature enables

client to connect to another listener if the initial connection to the first listener fails.

Enable client-side connect-time Failover by setting FAILOVER=ON in the corresponding client side TNS entry.

TESTRAC =
(DESCRIPTION =
(ADDRESS_LIST=
(LOAD_BALANCE = ON)
(FAILOVER = ON)
(ADDRESS = (PROTOCOL = TCP)(HOST = TESTRAC1-VIP)(PORT = 1521))
(ADDRESS = (PROTOCOL = TCP)(HOST = TESTRAC2-VIP)(PORT = 1521))
)
(CONNECT_DATA = (SERVICE_NAME = testdb.selectstarfrom.com))
)

If LOAD_BALANCE is set to on then clients randomly attempt connections to any nodes. If client made connection attempt to a down node, the client

needs to wait until it receives the information that the node is not accessible before trying alternate address in ADDRESS_LIST.

2. Transparent Application Failover (TAF)
If connection failure occurs after a connection is established, the connection fails over to other surviving nodes. Any uncommitted transactions are

rolled back and server side program variables and session properties will be lost. In some case the select statements automatically re-executed on

the new connection with the cursor positioned on the row on which it was positioned prior to the failover.

TESTRAC =
(DESCRIPTION =
(LOAD_BALANCE = ON)
(FAILOVER = ON)
(ADDRESS = (PROTOCOL = TCP)(HOST = TESTRAC1-VIP)(PORT = 1521))
(ADDRESS = (PROTOCOL = TCP)(HOST = TESTRAC1-VIP)(PORT = 1521))
(CONNECT_DATA =
(SERVICE_NAME = testdb.selectstarfrom.com)
(FAILOVER_MODE = (TYPE = SELECT)(METHOD = BASIC)(RETRIES = 180)(DELAY = 5))
)
)



Oracle DBA Interview Questions and Answers - RAC - 2
Oracle RAC Interview Questions and Answers

1. Where are the Clusterware files stored on a RAC environment?
The Clusterware is installed on each node (on an Oracle Home) and on the shared disks (the voting disks and the CSR file)

2. Where are the database software files stored on a RAC environment?
The base software is installed on each node of the cluster and the
database storage on the shared disks.

3. What kind of storage we can use for the shared Clusterware files?
- OCFS (Release 1 or 2)
- raw devices
- third party cluster file system such as GPFS or Veritas

4. What kind of storage we can use for the RAC database storage?
- OCFS (Release 1 or 2)
- ASM
- raw devices
- third party cluster file system such as GPFS or Veritas

5. What is a CFS?
A cluster File System (CFS) is a file system that may be accessed (read and write) by all members in a cluster at the same time. This implies that

all members of a cluster have the same view.

6. What is an OCFS2?
The OCFS2 is the Oracle (version 2) Cluster File System which can be used for the Oracle Real Application Cluster.

7. Which files can be placed on an Oracle Cluster File System?
- Oracle Software installation (Windows only)
- Oracle files (controlfiles, datafiles, redologs, files described by the bfile datatype)
- Shared configuration files (spfile)
- OCR and voting disk
- Files created by Oracle during runtime
Note: There are some platform specific limitations.

8. Do you know another Cluster Vendor?
HP Tru64 Unix, Veritas, Microsoft

9. How is possible to install a RAC if we don’t have a CFS?
This is possible by using a raw device.

10. What is a raw device?
A raw device is a disk drive that does not yet have a file system set up. Raw devices are used for Real Application Clusters since they enable the

sharing of disks.

11. What is a raw partition?
A raw partition is a portion of a physical disk that is accessed at the lowest possible level. A raw partition is created when an extended partition

is created and logical partitions are assigned to it without any formatting. Once formatting is complete, it is called cooked partition.

12. When to use CFS over raw?
A CFS offers:
- Simpler management
- Use of Oracle Managed Files with RAC
- Single Oracle Software installation
- Autoextend enabled on Oracle datafiles
- Uniform accessibility to archive logs in case of physical node failure
- With Oracle_Home on CFS, when you apply Oracle patches CFS guarantees that the updated Oracle_Home is visible to all nodes in the cluster.
Note: This option is very dependent on the availability of a CFS on your platform.

13. When to use raw over CFS?
- Always when CFS is not available or not supported by Oracle.
- The performance is very, very important: Raw devices offer best performance without any intermediate layer between Oracle and the disk.
Note: Autoextend fails on raw devices if the space is exhausted. However the space could be added online if needed.

14. What CRS is?
Oracle RAC 10g Release 1 introduced Oracle Cluster Ready Services (CRS), a platform-independent set of system services for cluster environments. In

Release 2, Oracle has renamed this product to Oracle Clusterware.

15. What is VIP IP used for?
It returns a dead connection IMMIDIATELY, when its primary node fails. Without using VIP IP, the clients have to wait around 10 minutes to receive

ORA-3113: “end of file on communications channel”. However, using Transparent Application Failover (TAF) could avoid ORA-3113.

16. Why we need to have configured SSH or RSH on the RAC nodes?
SSH (Secure Shell,10g+) or RSH (Remote Shell, 9i+) allows “oracle” UNIX account connecting to another RAC node and copy/ run commands as the local

“oracle” UNIX account.

17. Is the SSH, RSH needed for normal RAC operations?
No. SSH or RSH are needed only for RAC, patch set installation and clustered database creation.

18. Do we have to have Oracle RDBMS on all nodes?
Each node of a cluster that is being used for a clustered database will typically have the RDBMS and RAC software loaded on it, but not actual data

files (these need to be available via shared disk).

19. What are the restrictions on the SID with a RAC database? Is it limited to 5 characters?
The SID prefix in 10g Release 1 and prior versions was restricted to five characters by install/ config tools so that an ORACLE_SID of up to max of

5+3=8 characters can be supported in a RAC environment. The SID prefix is relaxed up to 8 characters in 10g Release 2, see bug 4024251 for more

information.

20. Does Real Application Clusters support heterogeneous platforms?
The Real Application Clusters do not support heterogeneous platforms in the same cluster.

21. Are there any issues for the interconnect when sharing the same switch as the public network by using VLAN to separate the network?
RAC and Clusterware deployment best practices suggests that the interconnect (private connection) be deployed on a stand-alone, physically separate,

dedicated switch. On big network the connections could be instable.

22. What is the Load Balancing Advisory?
To assist in the balancing of application workload across designated resources, Oracle Database 10g Release 2 provides the Load Balancing Advisory.

This Advisory monitors the current workload activity across the cluster and for each instance where a service is active; it provides a percentage

value of how much of the total workload should be sent to this instance as well as service quality flag.

23. How many nodes are supported in a RAC Database?
With 10g Release 2, we support 100 nodes in a cluster using Oracle Clusterware, and 100 instances in a RAC database. Currently DBCA has a bug where

it will not go beyond 63 instances. There is also a documentation bug for the max-instances parameter. With 10g Release 1 the Maximum is 63.

24. What is the Cluster Verification Utiltiy (cluvfy)?
The Cluster Verification Utility (CVU) is a validation tool that you can use to check all the important components that need to be verified at

different stages of deployment in a RAC environment.

25. What versions of the database can I use the cluster verification utility (cluvfy) with?
The cluster verification utility is release with Oracle Database 10g Release 2 but can also be used with Oracle Database 10g Release 1.

26. If I am using Vendor Clusterware such as Veritas, IBM, Sun or HP, do I still need Oracle Clusterware to run Oracle RAC 10g?
Yes. When certified, you can use Vendor Clusterware however you must still install and use Oracle Clusterware for RAC. Best Practice is to leave

Oracle Clusterware to manage RAC. For details see Metalink Note 332257.1 and for Veritas SFRAC see 397460.1.

27. Is RAC on VMW are supported?
Yes.

28. What is hangcheck timer used for ?
The hangcheck timer checks regularly the health of the system. If the system hangs or stop the node will be restarted automatically.

There are 2 key parameters for this module:

-> hangcheck-tick: this parameter defines the period of time between checks of system health. The default value is 60 seconds; Oracle recommends

setting it to 30seconds.

-> hangcheck-margin: this defines the maximum hang delay that should be tolerated before hangcheck-timer resets the RAC node.

29. Is the hangcheck timer still needed with Oracle RAC 10g?
Yes.

30. What files can I put on Linux OCFS2?
For optimal performance, you should only put the following files on Linux OCFS2:
- Datafiles
- Control Files
- Redo Logs
- Archive Logs
- Shared Configuration File (OCR)
- Voting File
- SPFILE

31. Is it possible to use ASM for the OCR and voting disk?
No, the OCR and voting disk must be on raw or CFS (cluster file system).

32. Can I change the name of my cluster after I have created it when I am using Oracle Clusterware?
No, you must properly uninstall Oracle Clusterware and then re-install.

33. What the O2CB is?
The O2CB is the OCFS2 cluster stack. OCFS2 includes some services. These services must be started before using OCFS2 (mount/ format the file

systems).

34. What the OCR file is used for?
OCR is a file that manages the cluster and RAC configuration.

35. What the Voting Disk file is used for?
The voting disk is nothing but a file that contains and manages information of all the node memberships.

36. What is the recommended method to make backups of a RAC environment?
RMAN to make backups of the database, dd to backup your voting disk and hard copies of the OCR file.

37. What command would you use to check the availability of the RAC system?
crs_stat -t -v (-t -v are optional)

38. What is the minimum number of instances you need to have in order to create a RAC?
You can create a RAC with just one server.

39. Name two specific RAC background processes
RAC processes are: LMON, LMDx, LMSn, LKCx and DIAG.

40.Can you have many database versions in the same RAC?
Yes, but Clusterware version must be greater than the greater database version.

41. What was RAC previous name before it was called RAC?
OPS: Oracle Parallel Server

42. What RAC component is used for communication between instances?
Private Interconnect.

43. What is the difference between normal views and RAC views?
A RAC view has the prefix ‘G’. For example, GV$SESSION instead of V$SESSION

44. Which command will we use to manage (stop, start) RAC services in command-line mode?
srvctl

45. How many alert logs exist in a RAC environment?
One for each instance.

46. What are Oracle Clusterware Components
Voting Disk — Oracle RAC uses the voting disk to manage cluster membership by way of a health check and arbitrates cluster ownership among the

instances in case of network failures. The voting disk must reside on shared disk.

Oracle Cluster Registry (OCR) — Maintains cluster configuration information as well as configuration information about any cluster database within

the cluster. The OCR must reside on shared disk that is accessible by all of the nodes in your cluster

47. How do you backup voting disk
#dd if=voting_disk_name of=backup_file_name

48. How do I identify the voting disk location
#crsctl query css votedisk

49. How do I identify the OCR file location
check /var/opt/oracle/ocr.loc or /etc/ocr.loc ( depends upon platform)
or
#ocrcheck

50. How do you backup the OCR
There is an automatic backup mechanism for OCR. The default location is : $ORA_CRS_HOME\cdata\"clustername"\
To display backups :
#ocrconfig -showbackup
To restore a backup :
#ocrconfig -restore
With Oracle RAC 10g Release 2 or later, you can also use the export command:
#ocrconfig -export -s online, and use -import option to restore the contents back.
With Oracle RAC 11g Release 1, you can do a manaual backup of the OCR with the command:
# ocrconfig -manualbackup

51. What is SCAN?
Single Client Access Name (SCAN) is s a new Oracle Real Application Clusters (RAC) 11g Release 2 feature that provides a single name for clients to

access an Oracle Database running in a cluster. The benefit is clients using SCAN do not need to change if you add or remove nodes in the cluster.

52. What are Oracle Clusterware processes for 10g on Unix and Linux
Cluster Synchronization Services (ocssd) — Manages cluster node membership and runs as the oracle user; failure of this process results in cluster

restart.

Cluster Ready Services (crsd) — The crs process manages cluster resources (which could be a database, an instance, a service, a Listener, a virtual

IP (VIP) address, an application process, and so on) based on the resource's configuration information that is stored in the OCR. This includes

start, stop, monitor and failover operations. This process runs as the root user

Event manager daemon (evmd) —A background process that publishes events that crs creates.

Process Monitor Daemon (OPROCD) —This process monitor the cluster and provide I/O fencing. OPROCD performs its check, stops running, and if the wake

up is beyond the expected time, then OPROCD resets the processor and reboots the node. An OPROCD failure results in Oracle Clusterware restarting the

node. OPROCD uses the hangcheck timer on Linux platforms.

RACG (racgmain, racgimon) —Extends clusterware to support Oracle- specific requirements and complex resources. Runs server callout scripts when FAN

events occur.

53. What are Oracle database background processes specific to RAC
•LMS—Global Cache Service Process
•LMD—Global Enqueue Service Daemon
•LMON—Global Enqueue Service Monitor
•LCK0—Instance Enqueue Process
To ensure that each Oracle RAC database instance obtains the block that it needs to satisfy a query or transaction, Oracle RAC instances use two

processes, the Global Cache Service (GCS) and the Global Enqueue Service (GES). The GCS and GES maintain records of the statuses of each data file

and each cached block using a Global Resource Directory (GRD). The GRD contents are distributed across all of the active instances.

54. How do you troubleshoot node reboot
Please check metalink ...
Note 265769.1 Troubleshooting CRS Reboots
Note.559365.1 Using Diagwait as a diagnostic to get more information for diagnosing Oracle Clusterware Node evictions.

55. Is ssh required for normal Oracle RAC operation ?
"ssh" are not required for normal Oracle RAC operation. However "ssh" should be enabled for Oracle RAC and patchset installation.

56. What is the purpose of Private Interconnect ?
Clusterware uses the private interconnect for cluster synchronization (network heartbeat) and daemon communication between the the clustered nodes.

This communication is based on the TCP protocol.
RAC uses the interconnect for cache fusion (UDP) and inter-process communication (TCP). Cache Fusion is the remote memory mapping of Oracle buffers,

shared between the caches of participating nodes in the cluster.

57. Why do we have a Virtual IP (VIP) in Oracle RAC?
Without using VIPs or FAN, clients connected to a node that died will often wait for a TCP timeout period (which can be up to 10 min) before getting

an error. As a result, you don't really have a good HA solution without using VIPs.

When a node fails, the VIP associated with it is automatically failed over to some other node and new node re-arps the world indicating a new MAC

address for the IP. Subsequent packets sent to the VIP go to the new node, which will send error RST packets back to the clients. This results in the

clients getting errors immediately.

58. What do you do if you see GC CR BLOCK LOST in top 5 Timed Events in AWR Report?
This is most likely due to a fault in interconnect network.
Check netstat -s
if you see "fragments dropped" or "packet reassemblies failed" , Work with your system administrator find the fault with network.

59. How many nodes are supported in a RAC Database?
10g Release 2, support 100 nodes in a cluster using Oracle Clusterware, and 100 instances in a RAC database.

60. Srvctl cannot start instance, I get the following error PRKP- 1001 CRS-0215, however sqlplus can start it on both nodes? How do you identify the

problem?
Set the environmental variable SRVM_TRACE to true.. And start the instance with srvctl. Now you will get detailed error stack.

61. What is the purpose of the ONS daemon?
The Oracle Notification Service (ONS) daemon is an daemon started by the CRS clusterware as part of the nodeapps. There is one ons daemon started per

clustered node.
The Oracle Notification Service daemon receive a subset of published clusterware events via the local evmd and racgimon clusterware daemons and

forward those events to application subscribers and to the local listeners.

This in order to facilitate:

a. the FAN or Fast Application Notification feature or allowing applications to respond to database state changes.

b. the 10gR2 Load Balancing Advisory, the feature that permit load balancing accross different rac nodes dependent of the load on the different

nodes. The rdbms MMON is creating an advisory for distribution of work every 30seconds and forward it via racgimon and ONS to listeners and

applications.

CRSCTL commands in Oracle 11g Release 2
How to shutdown CRS on all nodes and Disable CRS as ROOT user:
-------------------------------------------------------------
#crsctl stop crs
#crsctl disable crs

How to Enable CRS and restart CRS on all nodes as ROOT user:
-----------------------------------------------------------
#crsctl enable crs
#crsctl start crs

How to check VIP status is ONLINE / OFFLINE:
----------------------------------------
$crs_stat or
$crsctl stat res -t ------> 11gr2

How to Check current Version of Clusterware:
-------------------------------------------
$crsctl query crs activeversion

$crsctl query crs softwareversion [node_name]

How to Start & Stop CRS and CSS:
-------------------------------
$crsctl start crs
$crsctl stop crs

#/etc/init.d/init.crs start
#/etc/init.d/init.crs stop

#/etc/init.d/init.cssd stop
#/etc/init.d/init.cssd start

How to Enable & Disable CRS:
---------------------------
$crsctl enable crs
$crsctl disable crs

#/etc/init.d/init.crs enable
#/etc/init.d/init.crs disable

How to Check current status of CRS:
----------------------------------
$crsctl check crs

$crsctl check cluster [-node node_name]

How to Check CSS, CRS and EVMD:
------------------------------
$crsctl check cssd

$crsctl check crsd

$crsctl check evmd

How to List the Voting disks currently used by CSS:
--------------------------------------------------
$crsctl check css votedisk

$crsctl query css votedisk

How to Add and Delete any voting disk:
-------------------------------------
$crsctl add css votedisk <PATH>

$crsctl delete css votedisk <PATH>

How to start clusterware resources:
----------------------------------
$crsctl start resources

$crsctl stop resources

SRVCTL COMMANDS
How to STOP the Oracle RAC resources:
------------------------------------
#srvctl stop instance -d <database_name> -n <node_name>
#srvctl stop vip -n <node_name> -f

How to check current VIP configuration:
--------------------------------------
$srvctl config nodeapps -a

How to verify VIP status:
------------------------
$ifconfig -a

SCAN IP address in 11gR2 RAC
SCAN in RAC

Single Client Access Name (SCAN) eliminates the need to change TNSNAMES entry when nodes are added to or removed from the Cluster. RAC instances

register to SCAN listeners as remote listeners. Oracle recommends assigning 3 addresses to SCAN, which will create 3 SCAN listeners, though the

cluster has got dozens of nodes.. SCAN is a domain name registered to at least one and up to three IP addresses, either in DNS (Domain Name Service)

or GNS (Grid Naming Service). The SCAN must resolve to at least one address on the public network. For high availability and scalability, Oracle

recommends configuring the SCAN to resolve to three addresses.


How to start SCAN and SCAN Listener:
-----------------------------------
#$GRID_HOME/bin/srvctl start scan
#$GRID_HOME/bin/srvctl start scan_listener

How to STOP the SCAN LISTENER and the SCAN VIP resources:
--------------------------------------------------------
#$GRID_HOME/bin/srvctl stop scan_listener
#$GRID_HOME/bin/srvctl stop scan

How to check the STATUS of the SCAN LISTENER and the SCAN VIP resources:
-----------------------------------------------------------------------
#$GRID_HOME/bin/srvctl status scan_listener
SCAN listener LISTENER_SCAN1 is enabled
SCAN listener LISTENER_SCAN1 is not running
SCAN listener LISTENER_SCAN2 is enabled
SCAN listener LISTENER_SCAN2 is not running
SCAN listener LISTENER_SCAN3 is enabled
SCAN listener LISTENER_SCAN3 is not running

#$GRID_HOME/bin/srvctl status scan
SCAN VIP scan1 is enabled
SCAN VIP scan1 is not running
SCAN VIP scan2 is enabled
SCAN VIP scan2 is not running
SCAN VIP scan3 is enabled
SCAN VIP scan3 is not running

How to check SCAN-VIP in the resource file:
------------------------------------------
#$GRID_HOME/bin/srvctl config scan
SCAN name:rac-scan,Network: 1/10.100.10.0/255.255.255.0/eth1
SCAN VIP name: scan1, /rac-scan.localdomain.com/10.1000.10.21
SCAN VIP name: scan1, /rac-scan.localdomain.com/10.1000.10.22
SCAN VIP name: scan1, /rac-scan.localdomain.com/10.1000.10.23

How to check SCN IP address on DNS:
----------------------------------
$nslookup <scan-name>

$nslookup rac-scan.localdomain.com
Server: dns.localdomain.com
Address: 10.100.10.70#53

Name:rac-scan.localdomain.com
Address: 10.100.10.23
Name:rac-scan.localdomain.com
Address: 10.100.10.22
Name:rac-scan.localdomain.com
Address: 10.100.10.21

Oracle DBA Interview Questions and Answers - RAC
Oracle RAC Interview Questions and Answers

How does OCSSD starts first if voting disk & OCR resides in ASM Diskgroups?
You might wonder how CSSD, which is required to start the clustered ASM instance, can be started if voting disks are stored in ASM?
This sounds like a chicken-and-egg problem:
without access to the voting disks there is no CSS, hence the node cannot join the cluster.
But without being part of the cluster, CSSD cannot start the ASM instance.
To solve this problem the ASM disk headers have new metadata in 11.2:
you can use kfed to read the header of an ASM disk containing a voting disk.
The kfdhdb.vfstart and kfdhdb.vfend fields tell CSS where to find the voting file. This does not require the ASM instance to be up.
Once the voting disks are located, CSS can access them and joins the cluster.

What is gsdctl in RAC? list gsdctl commands in Oracle RAC?
GSDCTL stands for Global Service Daemon Control, we can use gsdctl commands to start, stop, and obtain the status of the GSD service on any platform.

The options for gsdctl are:-
$ gsdctl start -- To start the GSD service
$ gsdctl stop  -- To stop the GSD service
$ gsdctl stat  -- To obtain the status of the GSD service

Log file location for gsdctl:
$ ORACLE_HOME/srvm/log/gsdaemon_node_name.log

What is RAC?
RAC stands for Real Application cluster.
It is a clustering solution from Oracle Corporation that ensures high availability of databases by providing instance failover, media failover

features.
Oracle RAC is a cluster database with a shared cache architecture that overcomes the limitations of traditional shared-nothing and shared-disk

approaches to provide a highly scalable and available database solution for all the business applications.
Oracle RAC provides the foundation for enterprise grid computing.

What is Oracle RAC One Node?
Oracle RAC one Node is a single instance running on one node of the cluster while the 2nd node is in cold standby mode. If the instance fails for

some reason then RAC one node detect it and restart the instance on the same node or the instance is relocate to the 2nd node incase there is failure

or fault in 1st node. The benefit of this feature is that it provides a cold failover solution and it automates the instance relocation without any

downtime and does not need a manual intervention. Oracle introduced this feature with the release of 11gR2 (available with Enterprise Edition).

What is RAC and how is it different from non RAC databases?
Oracle Real Application clusters allows multiple instances to access a single database, the instances will be running on multiple nodes.
In Real Application Clusters environments, all nodes concurrently execute transactions against the same database.
Real Application Clusters coordinates each node's access to the shared data to provide consistency and integrity.

What are the advantages of RAC (Real Application Clusters)?
Reliability - if one node fails, the database won't fail
Availability - nodes can be added or replaced without having to shutdown the database
Scalability - more nodes can be added to the cluster as the workload increases

What is Oracle RAC One Node?
Oracle RAC one Node is a single instance running on one node of the cluster while the 2nd node is in cold standby mode. If the instance fails for

some reason then RAC one node detect it and restart the instance on the same node or the instance is relocate to the 2nd node incase there is failure

or fault in 1st node. The benefit of this feature is that it provides a cold failover solution and it automates the instance relocation without any

downtime and does not need a manual intervention. Oracle introduced this feature with the release of 11gR2 (available with Enterprise Edition).

What is Cache Fusion?
Oracle RAC is composed of two or more instances. When a block of data is read from datafile by an instance within the cluster and another instance is

in need of the same block, it is easy to get the block image from the instance which has the block in its SGA rather than reading from the disk. To

enable inter instance communication Oracle RAC makes use of interconnects. The Global Enqueue Service (GES) monitors and Instance enqueue process

manages the cache fusion.

What command would you use to check the availability of the RAC system?
crs_stat -t -v (-t -v are optional)

How do we verify that RAC instances are running?
SQL>select * from V$ACTIVE_INSTANCES;
The query gives the instance number under INST_NUMBER column,host_:instancename under INST_NAME column.

How can you connect to a specific node in a RAC environment?
tnsnames.ora ensure that you have INSTANCE_NAME specified in it.

Which is the "MASTER NODE" in RAC?
The node with the lowest node number will become master node and dynamic remastering of the resources will take place.
To find out the master node for particular resource, you can query v$ges_resource for MASTER_NODE column.
To find out which is the master node, you can see ocssd.log file and search for "master node number".
when the first master node fails in the cluster the lowest node number will become master node.

What components in RAC must reside in shared storage?
All datafiles, controlfiles, SPFIles, redo log files must reside on cluster-aware shred storage.

Give few examples for solutions that support cluster storage?
·ASM (automatic storage management),
·Raw disk devices,
·Network file system (NFS),
·OCFS2 and
·OCFS (Oracle Cluster Fie systems).

What are Oracle Cluster Components?
1.Cluster Interconnect (HAIP)
2.Shared Storage (OCR/Voting Disk)
3.Clusterware software
4.Oracle Kernel Components

What are Oracle RAC Components?
VIP, Node apps etc.

What are Oracle Kernel Components?
Basically Oracle kernel need to switched on with RAC On option when you convert to RAC, that is the difference as it facilitates few RAC bg process

like LMON,LCK,LMD,LMS etc.

How to turn on RAC?
# link the oracle libraries
$ cd $ORACLE_HOME/rdbms/lib
$ make -f ins_rdbms.mk rac_on
# rebuild oracle
$ cd $ORACLE_HOME/bin
$ relink oracle

Disk architechture in RAC?
SAN (Storage Area Networks) - generally using fibre to connect to the SAN
NAS (Network Attached Storage) - generally using a network to connect to the NAS using either NFS, ISCSI

What is Oracle Clusterware?
The Clusterware software allows nodes to communicate with each other and forms the cluster that makes the nodes work as a single logical server.
The software is run by the Cluster Ready Services (CRS) using the Oracle Cluster Registry (OCR) that records and maintains the cluster and node

membership information and the voting disk which acts as a tiebreaker during communication failures. Consistent heartbeat information travels across

the interconnect to the voting disk when the cluster is running.



Real Application Clusters
Oracle RAC is a cluster database with a shared cache architecture that overcomes the limitations of traditional shared-nothing and shared-disk

approaches to provide a highly scalable and available database solution for all your business applications. Oracle RAC provides the foundation for

enterprise grid computing.

Oracle’s Real Application Clusters (RAC) option supports the transparent deployment of a single database across a cluster of servers, providing fault

tolerance from hardware failures or planned outages. Oracle RAC running on clusters provides Oracle’s highest level of capability in terms of

availability, scalability, and low-cost computing.

One DB opened by multipe instances so the the db ll be Highly Available if an instance crashes.
Cluster Software. Oracles Clusterware or products like Veritas Volume Manager are required to provide the cluster support and allow each node to know

which nodes belong to the cluster and are available and with Oracle Cluterware to know which nodes have failed and to eject then from the cluster, so

that errors on that node can be cleared.

Oracle Clusterware has two key components Cluster Registry OCR and Voting Disk.

The cluster registry holds all information about nodes, instances, services and ASM storage if used, it also contains state information ie they are

available and up or similar.

The voting disk is used to determine if a node has failed, i.e. become separated from the majority. If a node is deemed to no longer belong to the

majority then it is forcibly rebooted and will after the reboot add itself again the the surviving cluster nodes.

What are the Oracle Clusterware key components?
Oracle Clusterware has two key components Cluster Registry OCR and Voting Disk.

What is Voting Disk and OCR?
Voting Disk
Oracle RAC uses the voting disk to manage cluster membership by way of a health check and arbitrates cluster ownership among the instances in case of

network failures. The voting disk must reside on shared disk.
A node must be able to access more than half of the voting disks at any time.
For example, if you have 3 voting disks configured, then a node must be able to access at least two of the voting disks at any time. If a node cannot

access the minimum required number of voting disks it is evicted, or removed, from the cluster.

Oracle Cluster Registry (OCR)
The cluster registry holds all information about nodes, instances, services and ASM storage if used, it also contains state information ie they are

available and up or similar.
The OCR must reside on shared disk that is accessible by all of the nodes in your cluster.

What are the administrative tasks involved with voting disk?
Following administrative tasks are performed with the voting disk :
1) Backing up voting disks
2) Recovering Voting disks
3) Adding voting disks
4) Deleting voting disks
5) Moving voting disks

Can you add voting disk online? Do you need voting disk backup?
Yes,  as per documentation, if you have multiple voting disk you can add online, but if you have only one voting disk , by that cluster will be down

as its lost you just need to start crs in exclusive mode and add the votedisk using
crsctl add votedisk <path>

What is the Oracle Recommendation for backing up voting disk?
Oracle recommends us to use the dd command to backup the voting disk with a minimum block size of 4KB.

How do we backup voting disks?
1) Oracle recommends that you back up your voting disk after the initial cluster creation and after we complete any node addition or deletion

procedures.
2) First, as root user, stop Oracle Clusterware (with the crsctl stop crs command) on all nodes. Then, determine the current voting disk by issuing

the following command:
crsctl query votedisk css
3) Then, issue the dd or ocopy command to back up a voting disk, as appropriate.
Give the syntax of backing up voting disks:-
On Linux or UNIX systems:
dd if=voting_disk_name of=backup_file_name
where,
voting_disk_name is the name of the active voting disk
backup_file_name is the name of the file to which we want to back up the voting disk contents
On Windows systems, use the ocopy command:
copy voting_disk_name backup_file_name

How do we verify an existing current backup of OCR?
We can verify the current backup of OCR using the following command : ocrconfig -showbackup

You have lost OCR disk, what is your next step?
The cluster stack will be down due to the fact that cssd is unable to maintain the integrity, this is true in 10g, From 11gR2 onwards, the crsd stack

will be down, the hasd still up and running. You can add the ocr back by restoring the automatic backup or import the manual backup,

What are the major RAC wait events?
In a RAC environment the buffer cache is global across all instances in the cluster and hence the processing differs.The most common wait events

related to this are gc cr request and gc buffer busy

GC CR request :the time it takes to retrieve the data from the remote cache
Reason: RAC Traffic Using Slow Connection or Inefficient queries (poorly tuned queries will increase the amount of data blocks requested by an Oracle

session. The more blocks requested typically means the more often a block will need to be read from a remote instance via the interconnect.)

GC BUFFER BUSY: It is the time the remote instance locally spends accessing the requested data block.

What do you do if you see GC CR BLOCK LOST in top 5 Timed Events in AWR Report?
This is most likely due to a fault in interconnect network.
Check netstat -s
if you see "fragments dropped" or "packet reassemblies failed" , Work with your system administrator find the fault with network.

How do you troubleshoot node reboot?
Please check metalink ...
Note 265769.1 Troubleshooting CRS Reboots
Note.559365.1 Using Diagwait as a diagnostic to get more information for diagnosing Oracle Clusterware Node evictions.

Srvctl cannot start instance, I get the following error PRKP-1001 CRS-0215, however sqlplus can start it on both nodes? How do you identify the

problem?
Set the environmental variable SRVM_TRACE to true.. And start the instance with srvctl. Now you will get detailed error stack.

What are Oracle Clusterware processes for 10g on Unix and Linux?
Cluster Synchronization Services (ocssd) — Manages cluster node membership and runs as the oracle user; failure of this process results in cluster

restart.

Cluster Ready Services (crsd) — The crs process manages cluster resources (which could be a database, an instance, a service, a Listener, a virtual

IP (VIP) address, an application process, and so on) based on the resource's configuration information that is stored in the OCR. This includes

start, stop, monitor and failover operations. This process runs as the root user

Event manager daemon (evmd) —A background process that publishes events that crs creates.

Process Monitor Daemon (OPROCD) —This process monitor the cluster and provide I/O fencing. OPROCD performs its check, stops running, and if the wake

up is beyond the expected time, then OPROCD resets the processor and reboots the node. An OPROCD failure results in Oracle Clusterware restarting the

node. OPROCD uses the hangcheck timer on Linux platforms.

RACG (racgmain, racgimon) —Extends clusterware to support Oracle-specific requirements and complex resources. Runs server callout scripts when FAN

events occur.

What are Oracle database background processes specific to RAC?
Oracle RAC is composed of two or more database instances. They are composed of Memory structures and background processes same as the single instance

database.Oracle RAC instances use two processes GES(Global Enqueue Service), GCS(Global Cache Service) that enable cache fusion.Oracle RAC instances

are composed of following background processes:
ACMS—Atomic Controlfile to Memory Service (ACMS)
GTX0-j—Global Transaction Process
LMON—Global Enqueue Service Monitor
LMD—Global Enqueue Service Daemon
LMS—Global Cache Service Process
LCK0—Instance Enqueue Process
RMSn—Oracle RAC Management Processes (RMSn)
RSMN—Remote Slave Monitor
To ensure that each Oracle RAC database instance obtains the block that it needs to satisfy a query or transaction, Oracle RAC instances use two

processes, the Global Cache Service (GCS) and the Global Enqueue Service (GES). The GCS and GES maintain records of the statuses of each data file

and each cached block using a Global Resource Directory (GRD). The GRD contents are distributed across all of the active instances.

What is GRD?
GRD stands for Global Resource Directory. The GES and GCS maintains records of the statuses of each datafile and each cahed block using global

resource directory.This process is referred to as cache fusion and helps in data integrity.

What is ACMS?
ACMS stands for Atomic Controlfile Memory Service.In an Oracle RAC environment ACMS is an agent that ensures a distributed SGA memory update(ie)SGA

updates are globally committed on success or globally aborted in event of a failure.

What is SCAN listener?
A scan listener is something that additional to node listener which listens the incoming db connection requests from the client which got through the

scan IP, it got end points configured to node listener where it routes the db connection requests to particular node listener.

SCAN IP can be disabled if not required. However SCAN IP is mandatory during the RAC installation. Enabling/disabling SCAN IP is mostly used in

oracle apps environment by the concurrent manager (kind of job scheduler in oracle apps).
Steps to disable the SCAN IP,
i.  Do not use SCAN IP at the client end.
ii. Stop scan listener
    srvctl stop scan_listener
iii.Stop scan
    srvctl stop scan (this will stop the scan vip's)
iv. Disable scan and disable scan listener
    srvctl disable scan

What are the different network components are in 10g RAC?
public, private, and vip components
Private interfaces is for intra node communication.
VIP is all about availability of application. When a node fails then the VIP component fail over to some other node, this is the reason that all

applications should based on vip components means tns entries should have vip entry in the host list

What is an interconnect network?
An interconnect network is a private network that connects all of the servers in a cluster. The interconnect network uses a switch/multiple switches

that only the nodes in the cluster can access.

What is the use of cluster interconnect?
Cluster interconnect is used by the Cache fusion for inter instance communication.

How can we configure the cluster interconnect?
· Configure User Datagram Protocol (UDP) on Gigabit Ethernet for cluster interconnects.
· On UNIX and Linux systems we use UDP and RDS (Reliable data socket) protocols to be used by Oracle Clusterware.
· Windows clusters use the TCP protocol.

What is the purpose of Private Interconnect?
Clusterware uses the private interconnect for cluster synchronization (network heartbeat) and daemon communication between the the clustered nodes.

This communication is based on the TCP protocol.
RAC uses the interconnect for cache fusion (UDP) and inter-process communication (TCP). Cache Fusion is the remote memory mapping of Oracle buffers,

shared between the caches of participating nodes in the cluster.

What is a virtual IP address or VIP?
A virtual IP address or VIP is an alternate IP address that the client connections use instead of the standard public IP address. To configure VIP

address, we need to reserve a spare IP address for each node, and the IP addresses must use the same subnet as the public network.

What is the use of VIP?
If a node fails, then the node's VIP address fails over to another node on which the VIP address can accept TCP connections but it cannot accept

Oracle connections.

Why do we have a Virtual IP (VIP) in Oracle RAC?
Without using VIPs or FAN, clients connected to a node that died will often wait for a TCP timeout period (which can be up to 10 min) before getting

an error. As a result, you don't really have a good HA solution without using VIPs.
When a node fails, the VIP associated with it is automatically failed over to some other node and new node re-arps the world indicating a new MAC

address for the IP. Subsequent packets sent to the VIP go to the new node, which will send error RST packets back to the clients. This results in the

clients getting errors immediately.

Give situations under which VIP address failover happens?
VIP addresses failover happens when the node on which the VIP address runs fails; all interfaces for the VIP address fails, all interfaces for the

VIP address are disconnected from the network.

What is the significance of VIP address failover?
When a VIP address failover happens, Clients that attempt to connect to the VIP address receive a rapid connection refused error .They don't have to

wait for TCP connection timeout messages.

What is the use of a service in Oracle RAC environment?
Applications should use the services feature to connect to the Oracle database. Services enable us to define rules and characteristics to control how

users and applications connect to database instances.

What are the characteristics controlled by Oracle services feature?
The characteristics include a unique name, workload balancing, failover options, and high availability.

What enables the load balancing of applications in RAC?
Oracle Net Services enable the load balancing of application connections across all of the instances in an Oracle RAC database.

What are the types of connection load-balancing?
Connection Workload management is one of the key aspects when you have RAC instances as you want to distribute the connections to specific

nodes/instance or those have less load.
There are two types of connection load-balancing:
1.Client Side load balancing (also called as connect time load balancing)
2.Server side load balancing (also called as Listener connection load balancing)

What is the difference between server-side and client-side connection load balancing?
Client-side balancing happens at client side where load balancing is done using listener.In case of server-side load balancing listener uses a load-

balancing advisory to redirect connections to the instance providing best service.

Client Side load balancing:- Oracle client side load balancing feature enables clients to randomize the connection requests among all the available

listeners based on their load.

An tns entry that contains all nodes entries and use load_balance=on (default its on) will use the connect time load balancing or client side load

balancing.

Sample Client Side TNS Entry:-

    finance =
    (DESCRIPTION =
         (ADDRESS = (PROTOCOL = TCP)(HOST = myrac2-vip)(PORT = 2042))
         (ADDRESS = (PROTOCOL = TCP)(HOST = myrac1-vip)(PORT = 2042))
         (ADDRESS = (PROTOCOL = TCP)(HOST = myrac3-vip)(PORT = 2042))
    (LOAD_BALANCE = yes)
    (CONNECT_DATA =
         (SERVER = DEDICATED)
         (SERVICE_NAME = FINANCE) (FAILOVER=ON)
    (FAILOVER_MODE =  (TYPE = SELECT) (METHOD = BASIC) (RETRIES = 180) (DELAY = 5))
    )
    )

Server side load balancing:- This improves the connection performance by balancing the number of active connections among multiple instances and

dispatchers. In a single instance environment (shared servers), the listener selects the least dispatcher to handle the incoming client requests. In

a rac environments, PMON is aware of all instances load and dispatchers , and depending on the load information PMON redirects the connection to the

least loaded node.

In a RAC environment, *.remote_listener parameter which is a tns entry containing all nodes addresses need to set to enable the load balance advisory

updates to PMON.

Sample Tns entry should be in an instances of RAC cluster,

    local_listener=LISTENER_MYRAC1
    remote_listener = LISTENERS_MYRACDB

What are the administrative tools used for Oracle RAC environments?
Oracle RAC cluster can be administered as a single image using the below
·       OEM (Enterprise Manager),
·       SQL*PLUS,
·       Server control (SRVCTL),
·       Cluster Verification Utility (CLUVFY),
·       DBCA,
·       NETCA

Name some Oracle Clusterware tools and their uses?
·OIFCFG - allocating and deallocating network interfaces.
·OCRCONFIG - Command-line tool for managing Oracle Cluster Registry.
·OCRDUMP - Identify the interconnect being used.
·CVU - Cluster verification utility to get status of CRS resources.

What is the difference between CRSCTL and SRVCTL?
crsctl manages clusterware-related operations:
    Starting and stopping Oracle Clusterware
    Enabling and disabling Oracle Clusterware daemons
    Registering cluster resources

srvctl manages Oracle resource–related operations:
    Starting and stopping database instances and services
    Also from 11gR2 manages the cluster resources like network,vip,disks etc

How do we remove ASM from a Oracle RAC environment?
We need to stop and delete the instance in the node first in interactive or silent mode.After that asm can be removed using srvctl tool as follows:
srvctl stop asm -n node_name
srvctl remove asm -n node_name
We can verify if ASM has been removed by issuing the following command:
srvctl config asm -n node_name

How do we verify that an instance has been removed from OCR after deleting an instance?
Issue the following srvctl command:
srvctl config database -d database_name
cd CRS_HOME/bin
./crs_stat

What are the modes of deleting instances from ORacle Real Application cluster Databases?
We can delete instances using silent mode or interactive mode using DBCA(Database Configuration Assistant).

What are the background process that exists in 11gr2 and functionality?
Process Name     Functionality
crsd     •The CRS daemon (crsd) manages cluster resources based on configuration information that is stored in Oracle Cluster Registry (OCR) for each

resource. This includes start, stop, monitor, and failover operations. The crsd process generates events when the status of a resource changes.
cssd     •Cluster Synchronization Service (CSS): Manages the cluster configuration by controlling which nodes are members of the cluster and by

notifying members when a node joins or leaves the cluster. If you are using certified third-party clusterware, then CSS processes interfaces with

your clusterware to manage node membership information. CSS has three separate processes: the CSS daemon (ocssd), the CSS Agent (cssdagent), and the

CSS Monitor (cssdmonitor). The cssdagent process monitors the cluster and provides input/output fencing. This service formerly was provided by Oracle

Process Monitor daemon (oprocd), also known as OraFenceService on Windows. A cssdagent failure results in Oracle Clusterware restarting the node.
diskmon     •Disk Monitor daemon (diskmon): Monitors and performs input/output fencing for Oracle Exadata Storage Server. As Exadata storage can be

added to any Oracle RAC node at any point in time, the diskmon daemon is always started when ocssd is started.
evmd     •Event Manager (EVM): Is a background process that publishes Oracle Clusterware events
mdnsd     •Multicast domain name service (mDNS): Allows DNS requests. The mDNS process is a background process on Linux and UNIX, and a service on

Windows.
gnsd     •Oracle Grid Naming Service (GNS): Is a gateway between the cluster mDNS and external DNS servers. The GNS process performs name resolution

within the cluster.
ons     •Oracle Notification Service (ONS): Is a publish-and-subscribe service for communicating Fast Application Notification (FAN) events
oraagent     •oraagent: Extends clusterware to support Oracle-specific requirements and complex resources. It runs server callout scripts when FAN

events occur. This process was known as RACG in Oracle Clusterware 11g Release 1 (11.1).
orarootagent     •Oracle root agent (orarootagent): Is a specialized oraagent process that helps CRSD manage resources owned by root, such as the

network, and the Grid virtual IP address
oclskd     •Cluster kill daemon (oclskd): Handles instance/node evictions requests that have been escalated to CSS
gipcd     •Grid IPC daemon (gipcd): Is a helper daemon for the communications infrastructure
ctssd     •Cluster time synchronisation daemon(ctssd) to manage the time syncrhonization between nodes, rather depending on NTP

Under which user or owner the process will start?
Component                     Name of the Process         Owner
Oracle High Availability Service         ohasd                 init, root
Cluster Ready Service (CRS)             Cluster Ready Services         root
Cluster Synchronization Service (CSS)         ocssd,cssd monitor, cssdagent     grid owner
Event Manager (EVM)                 evmd, evmlogger         grid owner
Cluster Time Synchronization Service (CTSS)     octssd                 root
Oracle Notification Service (ONS)         ons, eons             grid owner
Oracle Agent                     oragent             grid owner
Oracle Root Agent                 orarootagent             root
Grid Naming Service (GNS)             gnsd                 root
Grid Plug and Play (GPnP)             gpnpd                 grid owner
Multicast domain name service (mDNS)         mdnsd                 grid owner

What is the major difference between 10g and 11g RAC?
There is not much difference between 10g and 11gR (1) RAC. But there is a significant difference in 11gR2.

Prior to 11gR1(10g) RAC, the following were managed by Oracle CRS
    Databases
    Instances
    Applications
    Node Monitoring
    Event Services
    High Availability

From 11gR2(onwards) its completed HA stack managing and providing the following resources as like the other cluster software like VCS etc.
    Databases
    Instances
    Applications
    Cluster Management
    Node Management
    Event Services
    High Availability
    Network Management (provides DNS/GNS/MDNSD services on behalf of other traditional services) and SCAN – Single Access Client Naming method, HAIP
    Storage Management (with help of ASM and other new ACFS filesystem)
    Time synchronization (rather depending upon traditional NTP)
    Removed OS dependent hang checker etc, manages with own additional monitor process

What is hangcheck timer?
The hangcheck timer checks regularly the health of the system. If the system hangs or stop the node will be restarted automatically.
There are 2 key parameters for this module:
-> hangcheck-tick: this parameter defines the period of time between checks of system health. The default value is 60 seconds; Oracle recommends

setting it to 30seconds.
-> hangcheck-margin: this defines the maximum hang delay that should be tolerated before hangcheck-timer resets the RAC node.

State the initialization parameters that must have same value for every instance in an Oracle RAC database?
Some initialization parameters are critical at the database creation time and must have same values.Their value must be specified in SPFILE or PFILE

for every instance.The list of parameters that must be identical on every instance are given below:
ACTIVE_INSTANCE_COUNT
ARCHIVE_LAG_TARGET
COMPATIBLE
CLUSTER_DATABASE
CLUSTER_DATABASE_INSTANCE
CONTROL_FILES
DB_BLOCK_SIZE
DB_DOMAIN
DB_FILES
DB_NAME
DB_RECOVERY_FILE_DEST
DB_RECOVERY_FILE_DEST_SIZE
DB_UNIQUE_NAME
INSTANCE_TYPE (RDBMS or ASM)
PARALLEL_MAX_SERVERS
REMOTE_LOGIN_passWORD_FILE
UNDO_MANAGEMENT

---------------------------------------------------------------------------------------------------------------

What is RAC? What is the benefit of RAC over single instance database?
In Real Application Clusters environments, all nodes concurrently execute transactions against the same database. Real Application Clusters

coordinates each node's access to the shared data to provide consistency and integrity.
Benefits:
Improve response time
Improve throughput
High availability
Transparency


Advantages of RAC (Real Application Clusters)

Reliability - if one node fails, the database won't fail
Availability - nodes can be added or replaced without having to shutdown the database
Scalability - more nodes can be added to the cluster as the workload increases


What is a virtual IP address or VIP?

A virtual IP address or VIP is an alternate IP address that the client connections use instead of the standard public IP address. To configure VIP

address, we need to reserve a spare IP address for each node, and the IP addresses must use the same subnet as the public network.

What is the use of VIP?
If a node fails, then the node's VIP address fails over to another node on which the VIP address can accept TCP connections but it cannot accept

Oracle connections.
Give situations under which VIP address failover happens:-
VIP addresses failover happens when the node on which the VIP address runs fails, all interfaces for the VIP address fails, all interfaces for the

VIP address are disconnected from the network.
Using virtual IP we can save our TCP/IP timeout problem because Oracle notification service maintains communication between each nodes and listeners.

What is the significance of VIP address failover?
When a VIP address failover happens, Clients that attempt to connect to the VIP address receive a rapid connection refused error .They don't have to

wait for TCP connection timeout messages.

What is voting disk?
Voting Disk is a file that sits in the shared storage area and must be accessible by all nodes in the cluster. All nodes in the cluster registers

their heart-beat information in the voting disk, so as to confirm that they are all operational. If heart-beat information of any node in the voting

disk is not available that node will be evicted from the cluster. The CSS (Cluster Synchronization Service) daemon in the clusterware maintains the

heart beat of all nodes to the voting disk. When any node is not able to send heartbeat to voting disk, then it will reboot itself, thus help

avoiding the split-brain syndrome.

For high availability, Oracle recommends that you have a minimum of three or odd number (3 or greater) of votingdisks.

Voting Disk - is file that resides on shared storage and Manages cluster members.  Voting disk reassigns cluster ownership between the nodes in case

of failure.

The Voting Disk Files are used by Oracle Clusterware to determine which nodes are currently members of the cluster. The voting disk files are also

used in concert with other Cluster components such as CRS to maintain the clusters integrity.

Oracle Database 11g Release 2 provides the ability to store the voting disks in ASM along with the OCR. Oracle Clusterware can access the OCR and the

voting disks present in ASM even if the ASM instance is down. As a result CSS can continue to maintain the Oracle cluster even if the ASM instance

has failed.

How many voting disks are you maintaining ?



By default Oracle will create 3 voting disk files in ASM.

Oracle expects that you will configure at least 3 voting disks for redundancy purposes. You should always configure an odd number of voting disks >=

3. This is because loss of more than half your voting disks will cause the entire cluster to fail.

You should plan on allocating 280MB for each voting disk file. For example, if you are using ASM and external redundancy then you will need to

allocate 280MB of disk for the voting disk. If you are using ASM and normal redundancy you will need 560MB.

Why we need to keep odd number of voting disks ?
Oracle expects that you will configure at least 3 voting disks for redundancy purposes. You should always configure an odd number of voting disks >=

3. This is because loss of more than half your voting disks will cause the entire cluster to fail.


What are Oracle RAC software components?
Oracle RAC is composed of two or more database instances. They are composed of Memory structures and background processes same as the single instance

database.Oracle RAC instances use two processes GES(Global Enqueue Service), GCS(Global Cache Service) that enable cache fusion.Oracle RAC instances

are composed of following background processes:
ACMS—Atomic Controlfile to Memory Service (ACMS)
GTX0-j—Global Transaction Process
LMON—Global Enqueue Service Monitor
LMD—Global Enqueue Service Daemon
LMS—Global Cache Service Process
LCK0—Instance Enqueue Process
RMSn—Oracle RAC Management Processes (RMSn)
RSMN—Remote Slave Monitor

What are Oracle Clusterware processes for 10g ?
Cluster Synchronization Services (ocssd) — Manages cluster node membership and runs as the oracle user; failure of this process results in cluster

restart.
Cluster Ready Services (crsd) — The crs process manages cluster resources (which could be a database, an instance, a service, a Listener, a virtual

IP (VIP) address, an application process, and so on) based on the resource's configuration information that is stored in the OCR. This includes

start, stop, monitor and failover operations. This process runs as the root user
Event manager daemon (evmd) —A background process that publishes events that crs creates.
Process Monitor Daemon (OPROCD) —This process monitor the cluster and provide I/O fencing. OPROCD performs its check, stops running, and if the wake

up is beyond the expected time, then OPROCD resets the processor and reboots the node. An OPROCD failure results in Oracle Clusterware restarting the

node. OPROCD uses the hangcheck timer on Linux platforms.
RACG (racgmain, racgimon) —Extends clusterware to support Oracle-specific requirements and complex resources. Runs server callout scripts when FAN

events occur.

What are Oracle database background processes specific to RAC?
LMS—Global Cache Service Process
LMD—Global Enqueue Service Daemon
LMON—Global Enqueue Service Monitor
LCK0—Instance Enqueue Process
Oracle RAC instances use two processes, the Global Cache Service (GCS) and the Global Enqueue Service (GES). The GCS and GES maintain records of the

statuses of each data file and each cached block using a Global Resource Directory (GRD). The GRD contents are distributed across all of the active

instances.

What is Cache Fusion?
Transfor of data across instances  through private interconnect is called cachefusion.Oracle RAC is composed of two or more instances. When a block

of data is read from datafile by an instance within the cluster and another instance is in need of the same block,it is easy to get the block image

from the insatnce which has the block in its SGA rather than reading from the disk. To enable inter instance communication Oracle RAC makes use of

interconnects. The Global Enqueue Service(GES) monitors and Instance enqueue process manages the cahce fusion

What is SCAN? (11gR2 feature)
Single Client Access Name (SCAN) is s a new Oracle Real Application Clusters (RAC) 11g Release 2 feature that provides a single name for clients to

access an Oracle Database running in a cluster. The benefit is clients using SCAN do not need to change if you add or remove nodes in the cluster.

SCAN provides a single domain name via (DNS), allowing and-users to address a RAC cluster as-if it were a single IP address. SCAN works by replacing

a hostname or IP list with virtual IP addresses (VIP).

Single client access name (SCAN) is meant to facilitate single name for all Oracle clients to connect to the cluster database, irrespective of number

of nodes and node location. Until now, we have to keep adding multiple address records in all clients tnsnames.ora, when a new node gets added to or

deleted from the cluster.

Single Client Access Name (SCAN) eliminates the need to change TNSNAMES entry when nodes are added to or removed from the Cluster. RAC instances

register to SCAN listeners as remote listeners. Oracle recommends assigning 3 addresses to SCAN, which will create 3 SCAN listeners, though the

cluster has got dozens of nodes.. SCAN is a domain name registered to at least one and up to three IP addresses, either in DNS (Domain Name Service)

or GNS (Grid Naming Service). The SCAN must resolve to at least one address on the public network. For high availability and scalability, Oracle

recommends configuring the SCAN to resolve to three addresses.

What are SCAN components in a cluster?
1.SCAN Name
2.SCAN IPs (3)
3.SCAN Listeners (3)
What is FAN?
Fast application Notification as it abbreviates to FAN relates to the events related to instances,services and nodes.This is a notification mechanism

that Oracle RAc uses to notify other processes about the configuration and service level information that includes service status changes such as,UP

or DOWN events.Applications can respond to FAN events and take immediate action.

What is TAF?
TAF (Transparent Application Failover) is a configuration that allows session fail-over between different nodes of a RAC database cluster.
Transparent Application Failover (TAF). If a communication link failure occurs after a connection is established, the connection fails over to

another active node. Any disrupted transactions are rolled back, and session properties and server-side program variables are lost. In some cases, if

the statement executing at the time of the failover is a Select statement, that statement may be automatically re-executed on the new connection with

the cursor positioned on the row on which it was positioned prior to the failover.

After an Oracle RAC node crashes—usually from a hardware failure—all new application transactions are automatically rerouted to a specified backup

node. The challenge in rerouting is to not lose transactions that were "in flight" at the exact moment of the crash. One of the requirements of

continuous availability is the ability to restart in-flight application transactions, allowing a failed node to resume processing on another server

without interruption. Oracle's answer to application failover is a new Oracle Net mechanism dubbed Transparent Application Failover. TAF allows the

DBA to configure the type and method of failover for each Oracle Net client.
TAF architecture offers the ability to restart transactions at either the transaction (SELECT) or session level.

What are the requirements for Oracle Clusterware?
1. External Shared Disk to store Oracle Cluster ware file (Voting Disk and Oracle Cluster Registry - OCR)
2. Two netwrok cards on each cluster ware node (and three set of IP address) -
Network Card 1 (with IP address set 1) for public network
Network Card 2 (with IP address set 2) for private network (for inter node communication between rac nodes used by clusterware and rac database)
IP address set 3 for Virtual IP (VIP) (used as Virtual IP address for client connection and for connection failover)
3. Storage Option for OCR and Voting Disk - RAW, OCFS2 (Oracle Cluster File System), NFS, …..
Which enable the  load balancing of applications in RAC?
Oracle Net Services enable the load balancing of application connections across all of the instances in an Oracle RAC database.

How to find location of OCR file when CRS is down?
If you need to find the location of OCR (Oracle Cluster Registry) but your CRS is down.
When the CRS is down:
Look into “ocr.loc” file, location of this file changes depending on the OS:
On Linux: /etc/oracle/ocr.loc
On Solaris: /var/opt/oracle/ocr.loc
When CRS is UP:
Set ASM environment or CRS environment then run the below command:
ocrcheck

In 2 node RAC, how many NIC’s are r using ?
2 network cards on each clusterware node
Network Card 1 (with IP address set 1) for public network
Network Card 2 (with IP address set 2) for private network (for inter node communication between rac nodes used by clusterware and rac database)

In 2 node RAC, how many IP’s are r using ?
6 - 3 set of IP address
## eth1-Public:  2
## eth0-Private: 2
## VIP: 2

How to find IP’s information in RAC ?
Edit the /etc/hosts file as shown below:
# Do not remove the following line, or various programs
# that requires network functionality will fail.
127.0.0.1               localhost.localdomain localhost
## Public Node names
 192.168.10.11          node1-pub.hingu.net     node1-pub
192.168.10.22          node2-pub.hingu.net     node2-pub
## Private Network (Interconnect)
 192.168.0.11            node1-prv               node1-prv
192.168.0.22            node2-prv               node2-prv
## Private Network (Network Area storage)
 192.168.1.11            node1-nas               node1-nas
192.168.1.22            node2-nas               node2-nas
192.168.1.33            nas-server              nas-server
## Virtual IPs
 192.168.10.111          node1-vip.hingu.net     node1-vip
192.168.10.222          node2-vip.hingu.net     node2-vip

What is difference between RAC ip addresses ?
Public IP adress is the normal IP address typically used by DBA and SA to manage storage, system and database. Public IP addresses are reserved for

the Internet.
Private IP address is used only for internal clustering processing (Cache Fusion) (aka as interconnect). Private IP addresses are reserved for

private networks.
VIP is used by database applications to enable fail over when one cluster node fails. The purpose for having VIP is so client connection can be

failover to surviving nodes in case there is failure


Can application developer access the private ip ?
No. private IP address is used only for internal clustering processing (Cache Fusion) (aka as interconnect)

--------------------------------------------------------------------------------------------------------------
What is RAC?
RAC Architechture?

What is a SCAN Listener?

What is VIP?

What is TAF?

What is FAN?

What is LMON?

What is CACHE FUSION?

What is SPLIT BRAIN in RAC?

How Load balancing works in ORACLE RAC?

What is Voting Disk?
How many backups are there for Voting Disk?
WHY ODD NUMBER OF VOTING DISK IS USED?
How to take Voting Disk backup? Do you take Voting Disk backup?
If you lost Voting Disk, how do you Restore?

What is OCR?
How many backups are there for OCR?
How to take OCR backup? Do you take OCR backup?
If you lost  OCR, how do you Restore?

What is a Master Node?
How do you know which is the Master Node without connecting to Database?

Can we have Node 1 in SOLARIS OS and Node 2 in LINUX OS?

Commomnly used commands in RAC?

How to convert standalone database to RAC?

--------------------------------------------------------------------------------------------------------------

Log Directory Structure in RAC
Log Directory Structure in RAC
-------------------------------------------
Each component in the CRS (Cluster Ready Services) stack has its respective directories created under the CRS home.

$ORA_CRS_HOME/crs/log Contains trace files for the CRS resources.

$ORA_CRS_HOME/crs/init Contains trace files of the CRS daemon during startup. Good place to start with any CRS login problems.

$ORA_CRS_HOME/css/log The Cluster Synchronization (CSS) logs indicate all actions such as reconfigurations, missed check-ins, connects, and

disconnects from the client CSS listener. In some cases, the logger logs messages with the category of auth.crit for the reboots done by Oracle. This

could be used for checking the exact time when the reboot occurred.

$ORA_CRS_HOME/css/init Contains core dumps from the Oracle Cluster Synchronization Service daemon (OCSSd) and the process ID (PID) for the CSS daemon

whose death is treated as fatal. If abnormal restarts for CSS exist, the core files will have the format of core..

$ORA_CRS_HOME/evm/log Log files for the Event Volume Manager (EVM) and evmlogger daemons. Not used as often for debugging as the CRS and CSS

directories.

$ORA_CRS_HOME/evm/init PID and lock files for EVM. Core files for EVM should also be written here.

$ORA_CRS_HOME/srvm/log Log files for Oracle Cluster Registry (OCR), which contains the details at the Oracle cluster level.

$ORA_CRS_HOME//log Log files for Oracle Clusterware (known as the cluster alert log), which contains diagnostic messages at the Oracle cluster level.

This is available from Oracle database 10g R2.

RAC Commands
Cluster Related     Commands
---------------         --------
crs_stat -t        Shows HA resource status (hard to read)
crsstat            Ouptut of crs_stat -t formatted nicely
ps -ef|grep d.bin    crsd.bin evmd.bin ocssd.bin
crsctl check crs    CSS,CRS,EVM appears healthy
crsctl stop crs        Stop crs and all other services
crsctl disable crs*    Prevents CRS from starting on reboot
crsctl enable crs*    Enables CRS start on reboot
crs_stop -all        Stops all registered resources
crs_start -all        Starts all registered resources

NOTE
----
* These commands update the file /etc/oracle/scls_scr/<node>/root/crsstart which contains the string “enable” or “disable” as appropriate.

Database Related Commands
-------------------------
srvctl start instance -d <db_name> -i <inst_name>    Starts an instance
srvctl stop instance -d <db_name> -i <inst_name>    Stops an instance
srvctl status instance -d <db_name> -i <inst_name>    Checks an individual instance

srvctl start database -d <db_name>            Starts all instances
srvctl stop database -d <db_name>            Stops all instances, closes database
srvctl status database -d <db_name>            Checks status of all instances

srvctl start service -d <db_name> -s <service_name>    Starts a service
srvctl stop service -d <db_name> -s <service_name>    Stops a service
srvctl status service -d <db_name>            Checks status of a service

srvctl start nodeapps -n <node_name>            Starts gsd, vip, listener, and ons
srvctl stop nodeapps -n <node_name>            Stops gsd, vip and listener

BACKGROUND PROCESSES
----------------------------------
There are three main background processes you can see when doing a ps –ef|grep d.bin.  They are normally started by init during the operating system

boot process.  They can be started and stopped manually by issuing the command /etc/init.d/init.crs {start|stop|enable|disable}

/etc/rc.d/init.d/init.evmd
/etc/rc.d/init.d/init.cssd
/etc/rc.d/init.d/init.crsd

SERVICES
------------
Once the above processes are running, they will automatically start the following services in the following order if they are enabled.  This list

assumes you are using ASM and have a service set up for TAF/load balancing.

1.The nodeapps (gsd, VIP, ons, listener) are brought online.
2.The ASM instances are brought online.
3.The database instances are brought online.
4.Any defined services are brought online.

crsd fails to startup on 2nd node
ISSUE :
crsd fails to start on 2nd node after server reboot in 11gR2 RAC

NODE 1:

# crsctl check crs
CRS-4638: Oracle High Availability Services is online
CRS-4537: Cluster Ready Services is online
CRS-4529: Cluster Synchronization Services is online
CRS-4533: Event Manager is online
However, after both server rebooted cluster ready service on second node does not start, but on first node it works fine.

NODE 2:

# crsctl check crs
CRS-4638: Oracle High Availability Services is online
CRS-4535: Cannot communicate with Cluster Ready Services
CRS-4529: Cluster Synchronization Services is online
CRS-4533: Event Manager is online

# crs_stat -t
CRS-0184: Cannot communicate with the CRS daemon.



BACKUP ORACLE HOME AND INVENTORY
Oracle Home and Inventory Backup
-----------------------------------------
tar -cvf $ORACLE_HOME $ORACLE_HOME/oraInventory | gzip > Backup_Software_Version.tar.gz

Note:
tar -cvf <destination_location> <source_location>

ORACLE_HOME & ORACLE_CRS_HOME backup’s (for all nodes in RAC)

cd /u01/before_patch_backup

tar -cvf oracle_base_jun30.tar $ORACLE_BASE
tar -cvf oracle_home_jun30.tar $ORACLE_HOME
tar -cvf oracle_crs_home_jun30.tar $ORACLE_CRS_HOME

Controlfile Backup
---------------------
alter database backup controlfile to trace;

show parameter user_dump_dest
(go to udump dest and make the note of controlfile trace)