October 15, 2016

Oracle RAC Interview Questions/FAQs Part1

Oracle DBA RAC Interview Questions Part1


1. What is the use of RAC?

2. What are the prerequisites for RAC setup?


3. What are Oracle Clusterware/Daemon processes and what they do?

Ans:
ohasd, orarootagent, oragent, ocssd, crsd, ctsd, evmd, 

4. What are the special background processes for RAC (or) what is difference in stand-alone database & RAC database background processes?
DIAG, LCKn, LMD, LMSn, LMON 

5. What are structural changes in 11g R2 RAC?

Ans:
http://satya-racdba.blogspot.com/2010/07/new-features-in-9i-10g-11g-rac.html
Grid & ASM are on one home, 
Voting disk & ocrfile can be on the ASM,
SCAN,
By using srvctl, we can mange diskgroups, home, ons, eons, filesystem, srvpool, server, scan, scan_listener, gns, vip, oc4j,
GSD

6. What are the new features in 11g (R2) RAC?

Ans:
http://satya-racdba.blogspot.com/2010/07/new-features-in-9i-10g-11g-rac.html
Grid & ASM are on one home, 
Voting disk & ocrfile can be on the ASM,
SCAN,
By using srvctl, we can mange diskgroups, home, ons, eons, filesystem, srvpool, server, scan, scan_listener, gns, vip, oc4j,
GSD

7. What is cache fusion?

Ans:
Transferring of data between RAC instances by using private network. Cache Fusion is the remote memory mapping of Oracle buffers, shared between the caches of participating nodes in the cluster. 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.

8. What is the purpose of Private Interconnect?

Ans:
Clusterware uses the private interconnect for cluster synchronization (network heartbeat) and daemon communication between the clustered nodes. This communication is based on the TCP protocol. RAC uses the interconnect for cache fusion (UDP) and inter-process communication (TCP).

9. What are the Clusterware components?

Ans:
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. The daemon OCSSd manages the configuration info in OCR and maintains the changes to cluster in the registry.

Virtual IP (VIP) - 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.

crsd – Cluster Resource Services Daemon
cssd – Cluster Synchronization Services Daemon
evmd – Event Manager Daemon

10. What is OCR file?

Ans:
RAC configuration information repository that manages information about the cluster node list and instance-to-node mapping information. The OCR also manages information about Oracle Clusterware resource profiles for customized applications. 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. The daemon OCSSd manages the configuration info in OCR and maintains the changes to cluster in the registry.

11. How to take backup of OCR file?
Ans:
#ocrconfig -manualbackup
#ocrconfig -export file_name.dmp
#ocrdump -backupfile my_file
$cp -p -R /u01/app/crs/cdata /u02/crs_backup/ocrbackup/RAC1

12. How to recover OCR file?

Ans:
#ocrconfig -restore backup_file.ocr
#ocrconfig -import file_name.dmp

13. What is local OCR?

Ans:
/etc/oracle/local.ocr
/var/opt/oracle/local.ocr

14. How to check backup (location) of OCR files?

Ans:
#ocrconfig –showbackup

15. How do you identify the OCR file location?
Ans:
check /var/opt/oracle/ocr.loc or /etc/ocr.loc
ocrcheck

16. Who will manage OCR files?
Ans:
cssd will manage OCR.

17. Who will take backup of OCR files?
Ans:
crsd will take backup.

18. What is Voting file/disk and how many files should be there?
Ans:
Voting Disk File is a file on the shared cluster system or a shared raw device file. Oracle Clusterware uses the voting disk to determine which instances are members of a cluster. Voting disk is akin to the quorum disk, which helps to avoid the split-brain syndrome. 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.

Number of voting files must be odd i.e. 1, 3, 5 etc.

19. How to take backup of voting file?
Ans:
dd if=/u02/ocfs2/vote/VDFile_0 of=$ORACLE_BASE/bkp/vd/VDFile_0
crsctl backup css votedisk         -- from 11g R2

20. How do I identify the voting disk location?

Ans:
crsctl query css votedisk

21. If voting disk/OCR file got corrupted and don’t have backups, how to get them?
Ans:
We have to install Clusterware.


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