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

Backing up Volumes Online
216 VERITAS Volume Manager Administrator’s Guide
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 “Backing Up Multiple Volumes Using Snapshots” on page 218 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:
# fsck -F vxfs /dev/vx/rdsk/diskgroup/snapshot
5. Use a backup utility or operating system command to copy the temporary volume to
tape, or to some other appropriate backup media.
When the backup is complete, you have three choices for what to do with the snapshot
volume:
◆ Reattach some or all ofthe plexes of thesnapshot volume with the original volume as
described in “Merging a Snapshot Volume (snapback)” on page 218. 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.
◆ Dissociate the snapshot volume entirely from the original volume as described in
“Dissociating a Snapshot Volume (snapclear)” on page 219. This may be useful if you
want to use the copy for other purposes such as testing or report generation.
◆ Remove the snapshot volume to save space with this command:
# vxedit [-g diskgroup] -rf rm snapshot