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307Administering volume snapshots
Full-sized instant snapshots
Full-sized instant snapshots
Full-sized instant snapshots are a variation on the third-mirror volume
snapshot model that make a snapshot volume available for access as soon as the
snapshot plexes have been created. The full-sized instant volume snapshot
model is illustrated in Figure 9-2.
Figure 9-2 Full-sized instant snapshot creation and usage in a backup cycle
To create an instant snapshot, you use the
vxsnap make command. This
command can either be applied to a suitably prepared empty volume that is to be
used as the snapshot volume, or it can be used to break off one or more
synchronized plexes from the original volume (which is similar to the way that
the
vxassist command creates its snapshots).
Unlike a third-mirror break-off snapshot created using the
vxassist command,
you can make a backup of a full-sized instant snapshot, instantly refresh its
contents from the original volume, or attach its plexes to the original volume,
without needing to completely synchronize the snapshot plexes from the
original volume.
VxVM uses a copy-on-write mechanism to ensure that the snapshot volume
preserves the contents of the original volume at the time that the snapshot is
taken. Any time that the original contents of the volume are about to be
overwritten, the original data in the volume is preserved on the snapshot
volume before the write proceeds. As time goes by, and the contents of the
Original
volume
vxsnap make
vxsnap dis
Independent
volume
Back up to disk, tape or
other media. The snapshot
volume can also be used to
create a replica database or
file system when
synchronization is complete.
Snapshot
volume
Start
vxsnap reattach
vxsnap prepare
or
vxsnap split
vxsnap refresh
Backup
Cycle