Veritas Volume Manager 5.1 SP1 Administrator"s Guide (5900-1506, April 2011)

See “Implementing decision support” on page 399.
These applications use the Persistent FastResync feature of VxVM in conjunction
with linked break-off snapshots.
A volume snapshot represents the data that exists in a volume at a given time. As
such, VxVM does not have any knowledge of data that is cached by the overlying
file system, or by applications such as databases that have files open in the file
system. If you set the fsgen volume usage type on a volume that contains a Veritas
File System (VxFS), intent logging of the file system metadata ensures the internal
consistency of the file system that is backed up. For other file system types,
depending on the intent logging capabilities of the file system, there may be
potential inconsistencies between in-memory data and the data in the snapshot
image.
For databases, you must also use a suitable mechanism to ensure the integrity of
tablespace data when the volume snapshot is taken. Most modern database
software provides the facility to temporarily suspend file system I/O. For ordinary
files in a file system, which may be open to a wide variety of different applications,
there may be no way to ensure the complete integrity of the file data other than
by shutting down the applications and temporarily unmounting the file system.
In many cases, it may only be important to ensure the integrity of file data that
is not in active use when you take the snapshot.
Implementing off-host online backup
This section describes a procedure for implementing off-host online backup for
a volume in a private disk group. It outlines how to set up a regular backup cycle.
It is beyond the scope of this guide to describe how to configure a database to use
this procedure, or how to perform the backup itself.
395Configuring off-host processing
Implemention of off-host processing solutions