Veritas Volume Manager 5.0.1 Administrator's Guide, HP-UX 11i v3, First Edition, November 2009

The following section describes how to configure VxVM raw volumes and
SmartSync. The database uses the following types of volumes:
■ Data volumes are the volumes used by the database (control files and tablespace
files).
■ Redo log volumes contain redo logs of the database.
SmartSync works with these two types of volumes differently, so they must be
configured as described in the following sections.
To enable the use of SmartSync with database volumes in shared disk groups, set
the value of the volcvm_smartsync tunable to 1.
See “Tunable parameters for VxVM” on page 532.
Data volume configuration
The recovery takes place when the database software is started, not at system
startup. This reduces the overall impact of recovery when the system reboots.
Because the recovery is controlled by the database, the recovery time for the
volume is the resilvering time for the database (that is, the time required to replay
the redo logs).
Because the database keeps its own logs, it is not necessary for VxVM to do logging.
Data volumes should be configured as mirrored volumes without dirty region
logs. In addition to improving recovery time, this avoids any run-time I/O overhead
due to DRL, and improves normal database write access.
Redo log volume configuration
A redo log is a log of changes to the database data. Because the database does not
maintain changes to the redo logs, it cannot provide information about which
sections require resilvering. Redo logs are also written sequentially, and since
traditional dirty region logs are most useful with randomly-written data, they are
of minimal use for reducing recovery time for redo logs. However, VxVM can
reduce the number of dirty regions by modifying the behavior of its dirty region
logging feature to take advantage of sequential access patterns. Sequential DRL
decreases the amount of data needing recovery and reduces recovery time impact
on the system.
The enhanced interfaces for redo logs allow the database software to inform VxVM
when a volume is to be used as a redo log. This allows VxVM to modify the DRL
behavior of the volume to take advantage of the access patterns. Since the
improved recovery time depends on dirty region logs, redo log volumes should
be configured as mirrored volumes with sequential DRL.
See “Sequential DRL” on page 61.
Understanding Veritas Volume Manager
Dirty region logging
62