Veritas Volume Manager 4.1 Administrator's Guide (HP-UX 11i v3, February 2007)

SmartSync Recovery Accelerator
44 VERITAS Volume Manager Administrator’s Guide
SmartSync Recovery Accelerator
Note The SmartSync Recovery Accelerator feature is not supported by VxVM 4.1 on the
HP-UX 11i v3 platform.
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. If supported by the database vendor, the SmartSync feature uses an
extended interface between VxVM volumes and the database software to avoid
unnecessary work during mirror resynchronization. For example, Oracle
®
automatically
takes advantage of SmartSync to perform database resynchronization when it is available.
Note SmartSync is only applicable to databases that are configured on raw volumes. You
cannot use SmartSync with volumes that contain file systems. Use an alternative
solution such as DRL with such volumes.
You must configure volumes correctly to use SmartSync. For VxVM, there are two types of
volumes used by the database, as follows:
◆ Redo log volumes contain redo logs of the database.
◆ Data volumes are all other volumes used by the database (control files and tablespace
files).
SmartSync works with these two types of volumes differently, and they must be
configured correctly to take full advantage of the extended interfaces. The only difference
between the two types of volumes is that redo log volumes have dirty region logs, while
data volumes do not.
To enable the use of SmartSync with database volumes in shared disk groups, set the
value of the volcvm_smartsync tunable to 1. For a description of volcvm_smartsync,
see “Tunable Parameters” on page 411.
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 which
improves normal database write access.