OCR and VOTING DISKS

                                      Voting disk

  * Manages cluster Membership and
* Arbitrates cluster ownership b/w the nodes. (in case of n/w failures)
* File, resides in shared storage.
* High availability, Oracle recommends more then one voting disks.
       * an Odd number of voting disk.
* if use a single voting disk, then use mirroring at the file system level for redundancy.

* A node must be able to access more than half of the voting disks at any time.
Ex ; if you have five voting disks configured,
then a node must be able to access at least three 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.

Backing Up Voting Disks:
* However, back up the voting disks at the following times:
¦ After installation
¦ After adding nodes to or deleting nodes from the cluster
¦ After performing voting disk add or delete operations
when use dd command to take backup of voting disk, backup can be performed while CRS process is Active.
No need to stop the crsd.bin process before taking voting disk.

To checks voting disks availability
#CRS_home/bin/crsctl query css votedisk

To make a backup copy of the voting disk:
#dd if=voting_disk_name of=backup_file_name
If your voting disk is stored on a raw device, use the device name in place of voting_disk_name,
for example:
#dd if=/dev/sdd1 of=/tmp/voting.dmp

Recovering Voting Disks:
If a voting disk is damaged, no longer to use by the oracle clusterware, can recover if you have voting disk backup

#dd if=backup_file_name of=voting_disk_name

To add or remove a voting disk:
* You can dynamically add and remove voting disks after installing Oracle RAC.
                  1. Run the following command as the root user to add a voting disk:
#crsctl add css votedisk path
                  2. Run the following command as the root user to remove a voting disk:
#crsctl delete css votedisk path


Oracle Cluster Registry (OCR)

* Maintain cluster configuration info., as well configuration info abt any cluster database within the cluster.
* contains info such as which database instances run on which nodes and which services run on which databases.
* OCR resides on shared storage that is accessible by all the nodes in the cluster.
* Oracle clusterware can multiplex, or maintain multiple copies of OCR.
* Oracle recommands for this feature to ensure high availability.

These Oracle Clusterware components require the following additional disk space:
       * Two Oracle Clusterware Registry files, 280 MB each, or 560 MB total disk space
       * Three voting disk files, 280 MB each, or 840 MB total disk space

Backing up of Oracle Cluster Registry(OCR):
* Oracle Clusterware automatically creates OCR backups every 4 hours.
*At any one time, Oracle Clusterware always retains the latest 3 backup copies of the OCR that are
4 hours old,
1 day old and
1 week old.
Default Location in RHEL:
CRS_home/cdata/cluster_name (or)
/u001/app/grid_home/11.2.0/grid/cdata/scanname

To find the most recent backup of the OCR:
#CRS_home/bin/ocrconfig -showbackup

OCR log location:
/001/app/grid_home/11.2.0/grid/log/servername/client