Veritas Storage Foundation Intelligent Storage Provisioning 5.0 Solutions Guide, HP-UX 11i v3, First Edition, May 2008

27Off-host processing solutions
Implementing off-host processing solutions
Figure 4-1 Example implementation of off-host processing
Note: A volume snapshot represents the data that exists in a volume at a given
point in 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 the fsgen volume usage type is set 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 potentially be inconsistencies between in-memory data and the data
in the snapshot image.
For databases, a suitable mechanism must additionally be used to ensure the
integrity of tablespace data when the volume snapshot is taken. The facility to
temporarily suspend file system I/O is provided by most modern database
software. 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 at the time that you take the
snapshot.
Disks containing primary
volumes used to hold
production databases or file
systems
Disks containing snapshot
volumes used to implement
off-host processing solutions
SCSI or Fibre Channel
connectivity
OHP host
Primary host