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

Creating Traditional Third-Mirror Break-Off Snapshots
304 VERITAS Volume Manager Administrator’s Guide
Reattaching a Snapshot Volume (vxassist snapback)
Note The information in this section does not apply to RAID-5 volumes unless they have
been converted to a special layered volume layout by the addition of a DCO and
DCO volume. See “Adding a Version 0 DCO and DCO Volume” on page 307 for
details.
Snapback merges a snapshot copy of a volume with the original volume. One or more
snapshot plexes are detached from the snapshot volume and re-attached to the original
volume. The snapshot volume is removed if all its snapshot plexes are snapped back. This
task resynchronizes the data in the volume so that the plexes are consistent.
Note To enhance the efficiency of the snapback operation, enable FastResync on the
volume before taking the snapshot, as described in “Enabling FastResync on a
Vol um e” on page 252.
To merge one snapshot plex with the original volume, use the following command:
# vxassist [-g diskgroup] snapback snapshot
where snapshot is the snapshot copy of the volume.
To merge all snapshot plexes in the snapshot volume with the original volume, use the
following command:
# vxassist [-g diskgroup] -o allplexes snapback snapshot
To merge a specified number of plexes from the snapshot volume with the original
volume, use the following command:
# vxassist [-g diskgroup] snapback nmirror=number snapshot
Here the nmirror attribute specifies the number of mirrors in the snapshot volume that
are to be re-attached.
Once the snapshot plexes have been reattached and their data resynchronized, they are
ready to be used in another snapshot operation.
By default, the data in the original volume is used to update the snapshot plexes that have
been re-attached. To copy the data from the replica volume instead, use the following
command:
# vxassist [-g diskgroup] -o resyncfromreplica snapback snapshot
Caution Always unmount the snapshot volume (if mounted) before performing a
snapback. In addition, you must unmount the file system corresponding to the
primary volume before using the resyncfromreplica option.