VERITAS FlashSnap Point-In-Time-Copy Solutions Administrator's Guide

Chapter 1, Point-In-Time Copy Solutions
VERITAS Software Used in Point-In-Time Copy Scenarios
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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.
For more information, 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.
For more information, 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 since a previous Storage Checkpoint was taken.
Storage Checkpoints have the following important features:
◆ Storage Checkpoints persist across system reboots and crashes.
◆ A Storage Checkpoint can preserve not only file system metadata and the directory hierarchy
of the file system, but also user data as it existed when the Storage Checkpoint was taken.