Veritas Storage Foundation 5.1 SP1 Advanced Features Administrator"s Guide (5900-1503, April 2011)

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.
The examples provided in this document illustrate how to perform this operation.
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.
Choices for snapshot resynchronization
When a snapshot volume is reattached to its original volume within a shared disk
group, there are two choices for resynchronizing the data in the volume:
■ Resynchronize the snapshot from the original volume—updates the snapshot
with data from the primary volume that has changed since the snapshot was
taken. The snapshot is then again ready to be taken for the purposes of backup
or decision support.
■ Resynchronize the original volume from the snapshot—updates the original
volume with data from the snapshot volume that has changed since the
snapshot was taken. This may be necessary to restore the state of a corrupted
database or file system, or to implement upgrades to production software, and
is usually much quicker than using alternative approaches such as full
restoration from backup media.
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.
Understanding point-in-time copy methods
About point-in-time copy technology
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