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

Chapter 1, Understanding VERITAS Volume Manager

FastResync

Note You need a VERITAS FlashSnap

or FastResync license to use this feature.

Note The FastResync feature is not supported by VxVM 4.1 on the HP-UX 11i v3

platform.

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 clustered VxVM 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.

For details of how to enable FastResync on a per-volume basis, see “Enabling FastResync

on a Volume” on page 252.

FastResync Enhancements

FastResync provides two fundamental 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.

◆ FastResync allows you to refresh and re-use snapshots rather than discard them. You

can quickly re-associate (snapback) snapshot plexes with their original volumes. This

reduces the system overhead required to perform cyclical operations such as backups

that rely on the snapshot functionality of VxVM.