Veritas Volume Manager 4.1 Administrator's Guide (HP-UX 11i v3, February 2007)

Chapter 1, Understanding VERITAS Volume Manager

FastResync

How Persistent FastResync Works with Snapshots

Persistent FastResync uses a map in a DCO volume on disk to implement change tracking.

As for Non-Persistent FastResync, each bit in the map represents a contiguous number of

blocks in a volume’s address space.

“Mirrored Volume with Persistent FastResync Enabled” on page 53 shows an example of a

mirrored volume with two plexes on which Persistent FastResync is enabled. Associated

with the volume are a DCO object and a DCO volume with two plexes.

Mirrored Volume with Persistent FastResync Enabled

To create a traditional third-mirror snapshot or an instant (copy-on-write) snapshot, the

vxassist snapstart or vxsnap make operation respectively is performed on the

volume. This sets up a snapshot plex in the volume and associates a disabled DCO plex

with it, as shown in “Mirrored Volume After Completion of a snapstart Operation” on

page 54.

Mirrored Volume

Data Plex

DCO Volume

Data Plex Data Change Object

DCO DCO

Plex Plex