Veritas Storage Foundation Intelligent Storage Provisioning 5.0.1 Administrators Guide, HP-UX 11i v3, First Edition, November 2009

of the volume whose snapshot is being taken. A snapshot volume can be created
in either a data pool or in a clone pool.
■ Linked break-off snapshot volumes differ from full-sized instant snapshots
in that they can be set up in a different disk group from the data volume. This
makes them especially suitable for off-host processing applications where you
may want to create the snapshot on storage with different characteristics from
that used for the data volumes.
■ Space-optimized instant snapshots require less space than a full-sized instant
snapshot but they cannot be dissociated from their original volume nor can
they be moved into a different disk group. A space-optimized snapshot uses a
storage pool or cache, which can be shared by one or more other
space-optimized snapshots. You must set up the cache and the space-optimized
snapshot volume in advance of creating any space-optimized snapshots.
See “Creating instant snapshots” on page 107.
For details of how to use volume snapshots to implement off-host online backup,
see the Veritas Storage Foundation Intelligent Storage Provisioning Solutions Guide.
For more information about instant volume snapshot features, see the section
“Understanding Veritas Volume Manager” in the Veritas Volume Manager
Administrator’s Guide.
Full details of how to recover from failures of instant snapshot commands may
be found in the “Recovery from failure of instant snapshot operations” section
of the Veritas Volume Manager Troubleshooting Guide.
Most VxVM commands require superuser or equivalent privileges.
Limitations of volume snapshots
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
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
Administering instant snapshots
Limitations of volume snapshots
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