VERITAS Volume Manager 4.1 Administrator's Guide

Understanding VERITAS Volume Manager

SmartSync Recovery Accelerator

Chapter 148

SmartSync Recovery Accelerator

The SmartSync feature of 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. 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.

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 as described

in “Tuning VxVM” on page 406. See “volcvm_smartsync” on page 412 for

more information about this tunable.

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).