350Administering volume snapshots

Creating traditional third-mirror break-off snapshots

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 351 for details.

2Choose 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.

3Create 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 352 for more information.

4Use 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

5If 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” on page 352. 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” on page 354. 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