Hardware manual

Group Administration Advanced volume operations
10–6
Decreasing the reported size of a volume
You can decrease the reported size of the volume, while the volume remains online. Decreasing the size of a
volume is sometimes called “shrinking” a volume.
See About reported volume size on pa
ge 10-5 for information on the impact of changing the reported size of a
volume.
Caution: If you decre
ase a volume size to less than the amount of space currently in use, you can lose data.
You cannot use the Group Manager GUI to decrease the reported size
of a volume. Instead, you must use the
following Group Manager CLI command:
volume select volume_name shrink size
See the CLI Reference manual for more information about using CLI commands.
About template volumes and thin clones
Some computing environments use multiple volumes that contain a large amount of common data. For example,
some environments clone a standard volume and create multiple “boot volumes” that administrators use to boot
different client computers. Most of the data is common to all the volumes; only a small portion of volume space
contains unique data. Because each boot volume consumes pool space for the common data, the group is storing
multiple copies of the same data, which is not an efficient utilization of space.
To use pool space more efficiently, instead
of
cloning standard volumes, you can create one volume and populate it
with the common data. After you convert the volume to a template volume, you can create multiple thin clone
volumes and then write to each thin clone to make it unique. For example, you can add data such as a page file to a
thin clone.
Because a thin clone shares the common
data
in the template volume, each thin clone only consumes the space
needed to store the differences (or deltas) between the thin clone and the template volume.
Initially, a template volume and thin clone are identical in reported size and content. Because the group allocates
space to the
new thin clone in the same way it allocates space to a new standard, thin provisioned volume, only the
minimum volume reserve is consumed from free pool space.
When initiators write data to a thin clone, space is consumed from
free volume reserve. As needed, the group
allocates additional volume reserve to the thin clone, up to the maximum in-use space setting for the thin clone.
You can also modify the thin clone and change the data that the thin clone shares with
the template volume.
However, the data in the template volume is always preserved because a template volume is read-only. Group
Manager tracks the amount of data that is shared between each thin clone and template volume and displays it in
the Volume Status window.
See Space considerations for template volumes and
thin clone
s on page 10-7.
With a few exceptions, all normal volume operations apply
to template volumes and thin clones. See Restrictions
on template volumes and thin clone
s on page 10-8.
Thin clones are considered attached to the template volume and cannot exist without it, si
milar to how snapshots
depend on the base volume.