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319Administering volume snapshots
Creating instant snapshots
Creating instant snapshots
Note: You need a full license to use this feature.
VxVM allows you to make instant snapshots of volumes by using the
vxsnap
command.
Note: The information in this section also applies to RAID-5 volumes that have
been converted to a special layered volume layout by the addition of a DCO and
DCO volume. See “Using a DCO and DCO volume with a RAID-5 volume” on
page 277 for details.
A plex in a full-sized instant snapshot requires as much space as the original
volume. If you instead make a space-optimized instant snapshot of a volume,
this only requires enough storage to record the original contents of the parent
volume as they are changed during the life of the snapshot.
The recommended approach to performing volume backup from the command
line, or from a script, is to use the
vxsnap command. The vxsnap prepare and
make tasks allow you to back up volumes online with minimal disruption to
users.
The vxsnap prepare step creates a DCO and DCO volume and associates this
with the volume. It also enables Persistent FastResync on the volume.
The vxsnap make step creates an instant snapshot that is immediately available
for making a backup. After the snapshot has been taken, read requests for data
in the original volume are satisfied by reading either from a non-updated region
of the original volume, or from the copy of the original contents of an updated
region that have been recorded by the snapshot.
Note: Synchronization of a full-sized instant snapshot from the original volume
is enabled by default. If you specify the
syncing=no attribute to vxsnap make,
this disables synchronization, and the contents of the instant snapshot are
unlikely ever to become fully synchronized with the contents of the original
volume at the point in time that the snapshot was taken. If you wish to move an
instant snapshot volume to another disk group for export to another machine
for off-host processing, or to turn it into an independent volume, you must
ensure that the snapshot volume has been completely synchronized.
You can immediately retake a full-sized or space-optimized instant snapshot at
any time by using the
vxsnap refresh command. If a fully synchronized instant
snapshot is required, you must wait for the new resynchronization to complete.