vxassist snapwait

348Administering volume snapshots

Creating traditional third-mirror break-off snapshots

Creating traditional third-mirror break-off snapshots

VxVM provides third-mirror break-off snapshot images of volume devices using vxassist and other commands.

Note: To enhance the efficiency and usability of volume snapshots, turn on FastResync as described in “Enabling FastResync on a volume” on page 292. If Persistent FastResync is required, you must associate a version 0 DCO with the volume as described in “Adding a version 0 DCO and DCO volume” on page 356.

You need a full license to use this feature.

The procedure described in this section requires a plex that is large enough to store the complete contents of the volume. For details of a method that uses space-optimized snapshots, see “Creating instant snapshots” on page 319.

The recommended approach to performing volume backup from the command line, or from a script, is to use the vxassist command. The vxassist snapstart, snapwait, and snapshot tasks allow you to back up volumes online with minimal disruption to users.

The vxassist snapshot procedure consists of two steps:■Run vxassist snapstart to create a snapshot mirror.■Run vxassist snapshot to create a snapshot volume.

The vxassist snapstart step creates a write-only backup plex which gets attached to and synchronized with the volume. When synchronized with the volume, the backup plex is ready to be used as a snapshot mirror. The end of the update procedure is indicated by the new snapshot mirror changing its state to SNAPDONE. This change can be tracked by the

task, which waits until at least one of the mirrors changes its state to SNAPDONE. If the attach process fails, the snapshot mirror is removed and its space is released.

Note: If the snapstart procedure is interrupted, the snapshot mirror is automatically removed when the volume is started.

Once the snapshot mirror is synchronized, it continues being updated until it is detached. You can then select a convenient time at which to create a snapshot volume as an image of the existing volume. You can also ask users to refrain from using the system during the brief time required to perform the snapshot (typically less than a minute). The amount of time involved in