Veritas Storage Foundation 5.1 SP1 Advanced Features Administrator"s Guide (5900-1503, April 2011)

Traditional third-mirror break-off snapshots
Figure 17-1 shows the traditional third-mirror break-off volume snapshot model
that is supported by the vxassist command.
Figure 17-1
Third-mirror snapshot creation and usage
Start
Original volume
Snapshot mirror
Original volume
vxsassist snapclear
vxsassist
snapback
vxassist
snapstart
Refresh on snapback
Backup
cycle
Snapshot volume
Independent volume
Back up to disk, tape or
other media, or use to
replicate database or file
vxassist
snapshot
The vxassist snapstart command creates a mirror to be used for the snapshot,
and attaches it to the volume as a snapshot mirror. As is usual when creating a
mirror, the process of copying the volume’s contents to the new snapshot plexes
can take some time to complete. (The vxassist snapabort command cancels this
operation and removes the snapshot mirror.)
See “Full-sized instant snapshots” on page 202.
See “Space-optimized instant snapshots” on page 204.
When the attachment is complete, the vxassist snapshot command is used to
create a new snapshot volume by taking one or more snapshot mirrors to use as
its data plexes. The snapshot volume contains a copy of the original volume’s data
at the time that you took the snapshot. If more than one snapshot mirror is used,
the snapshot volume is itself mirrored.
The command, vxassist snapback, can be used to return snapshot plexes to the
original volume from which they were snapped, and to resynchronize the data in
the snapshot mirrors from the data in the original volume. This enables you to
refresh the data in a snapshot after you use it to make a backup. You can use a
variation of the same command to restore the contents of the original volume
from a snapshot previously taken.
201Administering volume snapshots
Traditional third-mirror break-off snapshots