Veritas Volume Manager 5.0 Administrator's Guide (September 2006)

320 Administering volume snapshots
Creating instant snapshots
If you specify the -b option to the vxsnap addmir command, you can use the
vxsnap snapwait command to wait for synchronization of the snapshot plexes to
complete, as shown in this example:
# vxsnap -g mydg snapwait vol1 nmirror=2
2 To create a third-mirror break-off snapshot, use the following form of the vxsnap
make command.
# vxsnap [-g diskgroup] make source=volume[/newvol=snapvol]\
{/plex=plex1[,plex2,...]|/nmirror=number]}
Either of the following attributes may be specified to create the new snapshot
volume, snapvol, by breaking off one or more existing plexes in the original volume:
plex Specifies the plexes in the existing volume that are to be broken off. This
attribute can only be used with plexes that are in the ACTIVE state.
nmirror Specifies how many plexes are to be broken off. This attribute can only
be used with plexes that are in the SNAPDONE state. (Such plexes could
have been added to the volume by using the
vxsnap addmir command.)
Snapshots that are created from one or more ACTIVE or SNAPDONE plexes in the
volume are already synchronized by definition.
For backup purposes, a snapshot volume with one plex should be sufficient.
For example, to create the instant snapshot volume, snap2myvol, of the volume,
myvol, in the disk group, mydg, from a single existing plex in the volume, use the
following command:
# vxsnap -g mydg make source=myvol/newvol=snap2myvol\
/nmirror=1
The next example shows how to create a mirrored snapshot from two existing plexes
in the volume:
# vxsnap -g mydg make source=myvol/newvol=snap2myvol\
/plex=myvol-03,myvol-04
3Use 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
4 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.
5 You now have the following choices of what to do with a third-mirror break-off
snapshot:
■ Refresh the contents of the snapshot. This creates a new point-in-time image of
the original volume ready for another backup. If synchronization was already in
progress on the snapshot, this operation may result in large portions of the
snapshot having to be resynchronized. See “Refreshing an instant snapshot” on
page 327 for details.