Veritas FlashSnap Point-In-Time Copy Solutions 5.0.1 Administrators Guide, HP-UX 11i v3, First Edition, November 2009

an additional plex to a mirrored volume. After the contents of the third-mirror
(or snapshot plex) had been synchronized from the original plexes of the volume,
it could be detached as a snapshot volume for use in backup or decision support
applications. Enhancements to the snapshot model allowed snapshot volumes to
contain more than a single plex, reattachment of a subset of a snapshot volume’s
plexes, and persistence of FastResync across system reboots or cluster restarts.
Release 4.0 of VxVM introduced instant snapshots, which offer advantages over
traditional third-mirror snapshots. The benefits of instant snapshots include
immediate availability for use, quick refreshment, and easier configuration and
administration. Full-sized instant snapshots are similar to third-mirror snapshots
in that they are the same length as the original volume.
Space-optimized instant snapshots require less space than full-sized snapshots
by recording changed regions in the original volume to a storage cache. As the
original volume is written to, VxVM preserves its data in the cache before the
write is committed.
See the Veritas Volume Manager Administrator’s Guide.
Disk group split/join
One or more volumes, such as snapshot volumes, can be split off into a separate
disk group and deported. They are then ready for importing on another host that
is dedicated to off-host processing. This host need not be a member of a cluster
but it must have access to the disks on which the volumes are configured. At a
later stage, the disk group can be deported, re-imported, and joined with the
original disk group, or with a different disk group.
Note: As space-optimized instant snapshots only record information about changed
regions in the original volume, they cannot be moved to a different disk group.
They are therefore unsuitable for the off-host processing applications that are
described in this document.
The contents of full-sized instant snapshots must be fully synchronized with the
unchanged regions in the original volume before such snapshots can be moved
into a different disk group and deported from a host.
See the Veritas Volume Manager Administrator’s Guide.
Storage Checkpoints
A Storage Checkpoint is a persistent image of a file system at a given instance in
time. Storage Checkpoints use a copy-on-write technique to reduce I/O overhead
by identifying and maintaining only those file system blocks that have changed
15Point-in-time copy solutions
Veritas software used in point-in-time copy scenarios