Veritas Volume Manager 5.1 SP1 Administrator"s Guide (5900-1506, April 2011)

See “Preparing a volume for DRL and instant snapshots” on page 359.
SmartSync recovery accelerator
The SmartSync feature of Veritas Volume Manager increases the availability of
mirrored volumes by only resynchronizing changed data. (The process of
resynchronizing mirrored databases is also sometimes referred to as resilvering.)
SmartSync reduces the time required to restore consistency, freeing more I/O
bandwidth for business-critical applications. SmartSync uses an extended interface
between VxVM volumes, VxFS file systems, and the Oracle database to avoid
unnecessary work during mirror resynchronization and to reduce the I/O overhead
of the DRL. For example, Oracle® automatically takes advantage of SmartSync to
perform database resynchronization when it is available.
Note: To use SmartSync with volumes that contain file systems, see the discussion
of the Oracle Resilvering feature of Veritas File System (VxFS).
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 496.
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.
59Understanding Veritas Volume Manager
Dirty region logging