A volume snapshot is an image of a Veritas Volume Manager (VxVM) volume at a given point in time. You can also take a snapshot of a volume set.
Volume snapshots allow you to make backup copies of your volumes online with minimal interruption to users. You can then use the backup copies to restore data that has been lost due to disk failure, software errors or human mistakes, or to create replica volumes for the purposes of report generation, application development, or testing.
Volume snapshots can also be used to implement off-host online backup.
Physically, a snapshot may be a full (complete bit-for-bit) copy of the data set, or it may contain only those elements of the data set that have been updated since snapshot creation. The latter are sometimes referred to as allocate-on-first-write snapshots, because space for data elements is added to the snapshot image only when the elements are updated (overwritten) for the first time in the original data set. Storage Foundation allocate-on-first-write snapshots are called space-optimized snapshots.