Veritas Volume Manager 5.1 SP1 Administrator"s Guide (5900-1506, April 2011)

Figure 1-34
Mirrored volume and snapshot volume after completion of a
snapshot operation
Data plex Data plex
Data plex
Mirrored volume
DCO
log plex
DCO volume
Data change object Snap object
DCO volume
Snapshot volume
Data change object Snap object
DCO
log plex
DCO
log plex
The DCO volume contains the single DCO plex that was associated with the
snapshot plex. If two snapshot plexes were taken to form the snapshot volume,
the DCO volume would contain two plexes. For space-optimized instant snapshots,
the DCO object and DCO volume are associated with a snapshot volume that is
created on a cache object and not on a VM disk.
Associated with both the original volume and the snapshot volume are snap
objects. The snap object for the original volume points to the snapshot volume,
and the snap object for the snapshot volume points to the original volume. This
allows VxVM to track the relationship between volumes and their snapshots even
if they are moved into different disk groups.
The snap objects in the original volume and snapshot volume are automatically
deleted in the following circumstances:
■ For traditional snapshots, the vxassist snapback operation is run to return
all of the plexes of the snapshot volume to the original volume.
■ For traditional snapshots, the vxassist snapclear operation is run on a
volume to break the association between the original volume and the snapshot
69Understanding Veritas Volume Manager
FastResync