Filter
Top Products
309Administering volume snapshots
Space-optimized instant snapshots
Space-optimized instant snapshots
Volume snapshots, such as those described in “Traditional third-mirror break-
off snapshots” on page 305 and “Full-sized instant snapshots” on page 307,
require the creation of a complete copy of the original volume, and use as much
storage space as the original volume.
Instead of requiring a complete copy of the original volume’s storage space,
space-optimized instant snapshots use a storage cache. The size of this cache
may be configured when the snapshot is created.
Note: A storage cache may be named and shared among several volumes in the
same disk group. If so, the size of the cache that is declared must be the same for
each volume’s space-optimized snapshot. You may find it convenient to
configure a single storage cache in a disk group that can be shared by all the
volumes in that disk group. See “Creating a shared cache object” on page 322 for
details.
When the original volume is written to, VxVM preserves the original data
contents in the cache before the write is committed. As the storage cache can be
configured to require much less storage than the original volume, it is referred
to as being space-optimized. If the cache becomes too full, you can configure
VxVM to grow the size of the cache automatically using any available free space
in the disk group.
The instant space-optimized snapshot model is illustrated in Figure 9-3.
Figure 9-3 Space-optimized instant snapshot creation and usage in a backup
cycle
Backup
Cycle
Original
volume
Back up to disk, tape or
other media.
Snapshot
volume
Start
vxsnap make
vxsnap prepare
vxsnap refresh