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

The FastResync feature (previously called Fast Mirror Resynchronization or FMR)

performs quick and efficient resynchronization of stale mirrors (a mirror that is

not synchronized). This increases the efficiency of the VxVM snapshot mechanism,

and improves the performance of operations such as backup and decision support

applications. Typically, these operations require that the volume is quiescent,

and that they are not impeded by updates to the volume by other activities on the

system. To achieve these goals, the snapshot mechanism in VxVM creates an exact

copy of a primary volume at an instant in time. After a snapshot is taken, it can

be accessed independently of the volume from which it was taken. In a Cluster

Volume Manager (CVM) environment with shared access to storage, it is possible

to eliminate the resource contention and performance overhead of using a snapshot

simply by accessing it from a different node.

See “Enabling FastResync on a volume” on page 338.

FastResync enhancements

FastResync provides the following enhancements to VxVM:

FastResync optimizes mirror resynchronization by keeping

track of updates to stored data that have been missed by a

mirror. (A mirror may be unavailable because it has been

detached from its volume, either automatically by VxVM as

the result of an error, or directly by an administrator using

a utility such as vxplex or vxassist. A returning mirror

is a mirror that was previously detached and is in the process

of being re-attached to its original volume as the result of

the vxrecover or vxplex att operation.) When a mirror

returns to service, only the updates that it has missed need

to be re-applied to resynchronize it. This requires much less

effort than the traditional method of copying all the stored

data to the returning mirror.

Once FastResync has been enabled on a volume, it does not

alter how you administer mirrors. The only visible effect is

that repair operations conclude more quickly.

Faster mirror

resynchronization

FastResync allows you to refresh and re-use snapshots

rather than discard them. You can quickly re-associate (snap

back) snapshot plexes with their original volumes. This

reduces the system overhead required to perform cyclical

operations such as backups that rely on the volume

snapshots.

Re-use of snapshots

Understanding Veritas Volume Manager

FastResync