Veritas Volume Manager 5.0.1 Administrator's Guide, HP-UX 11i v3, First Edition, November 2009

See “Comparison of snapshot features” on page 64.
A traditional snapshot volume is created from a snapshot plex by running the
vxassist snapshot operation on the volume. For instant snapshots, however,
the vxsnap make command makes an instant snapshot volume immediately
available for use. There is no need to run an additional command.
Figure 1-34 shows how the creation of the snapshot volume also sets up a DCO
object and a DCO volume for the snapshot volume.
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
71Understanding Veritas Volume Manager
FastResync