VERITAS Volume Manager 4.1 Administrator's Guide

Understanding VERITAS Volume Manager
FastResync
Chapter 156
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 Figure 1-34,
“Mirrored Volume and Snapshot Volume After Completion of a Snapshot
Operation,”, 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 objects in the original volume and snapshot volume 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 volume and the snapshot volume. If the
volumes are in different disk groups, snapclear must be run
separately on each volume.