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

FastResync of Volume Snapshots

316 VERITAS Volume Manager Administrator’s Guide

FastResync of Volume Snapshots

Note You need a VERITAS FlashSnap

or FastResync license to use this feature.

VxVM allows you to take multiple snapshots of your data at the level of a volume. A

snapshot volume contains a stable copy of a volume’s data at a given moment in time that

you can use for online backup or decision support. If FastResync is enabled on a volume,

VxVM uses a FastResync map to keep track of which blocks are updated in the volume and

in the snapshot. If the data in one mirror is not updated for some reason, it becomes

out-of-date, or stale, with respect to the other mirrors in the volume. The presence of the

FastResync map means that only those updates that the mirror has missed need be

reapplied to resynchronize it with the volume. A full, and therefore much slower,

resynchronization of the mirror from the volume is unnecessary.

The persistent form of FastResync ensures that FastResync maps survive both system

crashes and cluster restarts. When snapshot volumes are reattached to their original

volumes, FastResync allows the snapshot data to be quickly refreshed and re-used. If

Persistent FastResync is enabled on a volume in a private disk group, such incremental

resynchronization can happen even if the host is rebooted.

Persistent FastResync can track the association between volumes and their snapshot

volumes after they are moved into different disk groups. When the disk groups are

rejoined, this allows the snapshot plexes to be quickly resynchronized. Non-Persistent

FastResync cannot be used for this purpose.

For more information, see “Vol ume S nap shots” on page 45 and “FastResync” on page 49.

Disk Group Split and Join

Note You need a VERITAS FlashSnap

license to use this feature.

A volume, such as a snapshot volume, can be split off into a separate disk group and

deported. It is then ready for importing on another host that is dedicated to off-host

processing. This host need not be a member of a cluster but must have access to the disks.

At a later stage, the disk group can be deported, re-imported, and joined with the original

disk group or with a different disk group.

For more information, see “Reorganizing the Contents of Disk Groups” on page 155.