VERITAS Volume Manager 4.1 Administrator's Guide

Administering Volumes
Backing up Volumes Online
Chapter 8 311
If vxassist snapstart is not run in the background, it does not exit until
the mirror has been synchronized with the volume. The mirror is then
ready to be used as a plex of a snapshot volume. While attached to the
original volume, its contents continue to be updated until you take the
snapshot.
Use the nmirror attribute to create as many snapshot mirrors as you
need for the snapshot volume. For a backup, you should usually only
require the default of one.
It is also possible to make a snapshot plex from an existing plex in a
volume. See “Converting a Plex into a Snapshot Plex” on page 312 for
details.
Step 2. Choose a suitable time to create a snapshot. If possible, plan to take the
snapshot at a time when users are accessing the volume as little as
possible.
Step 3. Create a snapshot volume using the following command:
# vxassist [-g diskgroup] snapshot [nmirror=N] volume
snapshot
If required, use the nmirror attribute to specify the number of mirrors in
the snapshot volume.
For example, to create a snapshot of voldef, use the following command:
# vxassist [-g diskgroup] snapshot voldef snapvol
The vxassist snapshot task detaches the finished snapshot mirror,
creates a new volume, and attaches the snapshot mirror to it. This step
should only take a few minutes. The snapshot volume, which reflects the
original volume at the time of the snapshot is now available for backing
up, while the original volume continues to be available for applications
and users.
If required, you can make snapshot volumes for several volumes in a disk
group at the same time. See “Backing Up Multiple Volumes Using
Snapshots” on page 313 for more information.
Step 4. Use fsck (or some utility appropriate for the application running on the
volume) to clean the temporary volume’s contents. For example, you can
use this command:
# fsck vxfs /dev/vx/rdsk/diskgroup/snapshot