VERITAS Volume Manager 3.5 Administrator's Guide (September 2002)

FastResync

46 VERITAS Volume Manager Administrator’s Guide

When the snapstart operation isperformed on thevolume, this sets up a snapshot plex

in the volume and associates a disabled DCO plex with it, as shown in “Mirrored Volume

After Completion of a snapstart Operation.”

Mirrored Volume After Completion of a snapstart Operation

Multiple snapshot plexes and associated DCO plexes may be created in the volume by

re-running the snapstart operation. You can create up to a total of 32 plexes (data and

log) in a volume.

A snapshot volume can now be created from a snapshot plex by running the snapshot

operation on the volume. As illustrated in “Mirrored Volume and Snapshot Volume After

Completion of a snapshot Operation” on page 47, this also sets up a DCO object and a

DCO volume for the snapshot volume. The new DCO volume contains the single DCO

plex that was associated with the snapshot plex. If two snapshot plexes were taken to

form the snapshot volume, the DCO volume would contain two plexes.

Associated with both the original volume and the snapshot volume are snap objects. The

snap object for the original volume points to the snapshot volume, and the snap object for

the snapshot volume points to the original volume. This allows VxVM to track the

relationship between volumes and their snapshots even if they are moved into different

disk groups.

The snap objectsin theoriginal volumeand snapshotvolume are automatically deleted in

either of the following circumstances:

◆ The snapback operation is run to return all of the plexes of the snapshot volume to

the original volume.

◆ The snapclear operation is run on a volume to break the association between the

original volumeand the snapshot volume. Ifthe volumes are indifferent diskgroups,

snapclear must be run separately on each volume.

Mirrored Volume

Data Plex

DCO Volume

Data Plex

Data Change Object

DCO

Plex

Snapshot

Plex

Disabled

DCO

Plex