Veritas FlashSnap Point-In-Time Copy Solutions 5.0 AdministratorÆs Guide, HP-UX 11i v3, First Edition, May 2008

10 Point-in-time copy solutions
Software used in point-in-time copy scenarios
■ Veritas Volume Manager (VxVM) is a disk management subsystem that
supports disk striping, disk mirroring, and simplified disk management for
improved data availability and superior performance. The FlashSnap
functionality uses the persistent FastResync and Disk Group Split/Join
features of VxVM.
■ Veritas File System (VxFS) is a high-performance, fast-recovery file system
that is optimized for business-critical database applications and data-
intensive workloads. VxFS offers online administration, letting you perform
most frequently scheduled maintenance tasks (including online backup,
resizing, and file system changes) without interrupting data or system
availability. The FlashSnap functionality uses the Storage Checkpoints
feature of VxFS.
You can also use the following cluster-specific components with the sample
scenarios where required:
■ HP Serviceguard may be configured as the cluster monitor.
■ Veritas Clustering Functionality for VxVM (CVM) allows multiple hosts to
simultaneously access and manage a given set of disks that are under the
control of Veritas Volume Manager.
■ Veritas Cluster File System (CFS) allows cluster nodes to share access to the
same VxFS file system. CFS is especially useful for sharing read-intensive
data between cluster nodes.
Persistent FastResync of volume snapshots
Veritas Volume Manager allows you to take multiple snapshots of your data at
the level of a volume. A snapshot volume contains a stable copy of a volume’s
data at a given moment in time that you can use for online backup or decision
support. If persistent FastResync is enabled on a volume, VxVM uses a
FastResync map to keep track of which blocks are updated in the volume and in
the snapshot. If the data in one mirror is not updated for some reason, it
becomes out-of-date, or stale, with respect to the other mirrors in the volume.
The presence of the FastResync map means that only those updates that the
mirror has missed need be reapplied to resynchronize it with the volume. A full,
and therefore much slower, resynchronization of the mirror from the volume is
unnecessary.
When snapshot volumes are reattached to their original volumes, persistent
FastResync allows the snapshot data to be quickly refreshed and re-used.
Persistent FastResync uses disk storage to ensure that FastResync maps survive
both system and cluster crashes. If persistent FastResync is enabled on a volume
in a private disk group, incremental resynchronization can take place even if the
host is rebooted.