Storage Foundation for Oracle® RAC 7.3.1 Administrator's Guide - Linux

About the I/O fencing registration key format

The keys that the vxfen driver registers on the data disks and the coordinator disks consist of eight bytes. The key format is different for the coordinator disks and data disks.

The key format of the coordinator disks is as follows:

The vxfen driver uses this key format in both sybase mode of I/O fencing.

The key format of the data disks that are configured as failover disk groups under VCS is as follows:

where nID is the LLT node ID

For example: If the node ID is 1, then the first byte has the value as B ('A' + 1 = B).

The key format of the data disks configured as parallel disk groups under Cluster Volume Manager (CVM) is as follows:

where DGcount is the count of disk groups in the configuration (consumes four bytes).

By default, CVM uses a unique fencing key for each disk group. However, some arrays have a restriction on the total number of unique keys that can be registered. In such cases, you can use the same_key_for_alldgs tunable parameter to change the default behavior. The default value of the parameter is off. If your configuration hits the storage array limit on total number of unique keys, you can change the value to on using the vxdefault command as follows:

# vxdefault set same_key_for_alldgs on
# vxdefault list
KEYWORD              CURRENT-VALUE   DEFAULT-VALUE
...
same_key_for_alldgs  on              off
...

If the tunable is changed to on, all subsequent keys that the CVM generates on disk group imports or creates have '0000' as their last four bytes (DGcount is 0). You must deport and re-import all the disk groups that are already imported for the changed value of the same_key_for_alldgs tunable to take effect.