HP Veritas Volume Manager 5.0 -UX 11i v3 manual Full-sized instant snapshots

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 Figure 9-2.

Figure 9-2 Full-sized instant snapshot creation and usage in a backup cycle

Start vxsnap make

vxsnap prepare

Original volume

vxsnap reattach

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.

vxsnap refresh

Snapshot Backup

volume Cycle

vxsnap dis

or

vxsnap split

Independent

volume

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-writemechanism 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