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

Chapter 9, Administering Volume Snapshots
Creating Traditional Third-Mirror Break-Off Snapshots
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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 302 for details.
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.
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 “Creating Multiple Snapshots” on page 303 for more information.
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 with
a VxFS file system:
# fsck -F vxfs /dev/vx/rdsk/diskgroup/snapshot
5. If you require a backup of the data in the snapshot, use an appropriate utility or
operating system command to copy the contents of the snapshot to tape, or to some
other backup medium.
When the backup is complete, you have the following choices for what to do with the
snapshot volume:
◆ Reattach some or all of the plexes of the snapshot volume with the original volume as
described in “Reattaching a Snapshot Volume (vxassist snapback)” on page 304. If
FastResync was enabled on the volume before the snapshot was taken, this speeds
resynchronization of the snapshot plexes before the backup cycle starts again at
step 3.