READ ME before using the Veritas Storage Foundation™ 5.1 SP1 for Oracle RAC Administrator's Guide (April 2011)

3 About CVM and CFS in an SGeRAC Environment
Before installing SGeRAC, review the following information on CVM and CFS to better understand
the overall setup so you can plan your SGeRAC configuration. For more information on SGeRAC,
see Using Serviceguard Extension for RAC, Serviceguard Extension for RAC Version A.11.20
Release Notes and related SGeRAC White Papers published on the HP Business Support Center
(BSC) web site at: www.hp.com/go/hpux-serviceguard-docs → HP Serviceguard Extension for
RAC
About CVM and CFS in an SGeRAC Environment
Before installing SGeRAC, you can review concepts on CVM and CFS to better understand the
overall setup and plan your SGeRAC configuration.
About CVM
Review CVM configuration differences from VxVM and CVM recovery operations.
CVM Configuration Differences
CVM configuration differs from VxVM configuration in these areas:
• Configuration commands occur on the master node.
• Disk groups are created (could be private) and imported as shared disk groups.
• Disk groups are activated per node.
• Shared disk groups are automatically imported when CVM starts.
CVM Recovery
When a node leaves a cluster, it can leave some mirrors in an inconsistent state. The membership
change is communicated through GAB to the vxconfigd daemon, which automatically calls the
vxrecover utility with the -c option when necessary.
CVM supports both the FastResync option and dirty region logging (DRL) as optional features to
improve resynchronization performance. FastResync improves performance when reorganizing
volumes (moving, splitting, and joining disk groups). This is useful when performing off-host
processing. DRL speeds up resynchronization after a node failure.
Special considerations exist when using the DRL in an SGeRAC environment. As in a non-clustered
environment, the DRL in clusters exists on a log subdisk in a mirrored volume. The size of the DRL
in clusters is typically larger than in non-clustered systems. The log size depends on the volume
size and the number of nodes. The vxassist command automatically imports a sufficiently large
DRL.
You can reimport a private disk group as a shared disk group but the DRL for any mirrored volume
in the disk group is probably too small to accommodate maps for all the cluster nodes. Adding
nodes to the cluster can also result in too small a log size. In this situation, VxVM marks the log
invalid and performs full volume recovery instead of using DRL.
About CFS
Review CFS File System benefits, CFS configuration differences from VxFS and CFS recovery
operations.
CFS File System Benefits
Many features available in VxFS do not come into play in an SGeRAC environment because ODM
handles such features. CFS adds such features as high availability, consistency and scalability,
16 About CVM and CFS in an SGeRAC Environment