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

Chapter 9, Administering Volume Snapshots
Full-Sized Instant Snapshots
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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 “Full-Sized
Instant Snapshot Creation and Usage in a Backup Cycle.”
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
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