HP 3PAR StoreServ Concepts Guide: HP 3PAR OS 3.1.3

10 Reclaiming Unused Space
Overview
The HP 3PAR OS space consolidation features allow you to change the way that virtual volumes
are mapped to LDs in a CPG. Moving virtual volume regions from one LD to another enables you
to compact LDs, and free up disk space so that it can be reclaimed for use by the system. For more
information about virtual volumes, see “Virtual Volumes” (page 44).
Mapping is the relationship of LD regions to the virtual volume regions. Virtual volumes are made
up of multiple LDs, and each LD contains regions that are mapped to the virtual volume. All types
of volumes are created by mapping data from one or more LDs to the virtual volume. Figure 12
(page 52) shows how data is mapped in regions from LDs to a base volume.
Figure 12 Mapped in Regions from LDs to a Virtual Volume in Regions
LDs can be shared by multiple virtual volumes. As volumes are deleted, or as volume copy space
grows and then shrinks, LDs use space less efficiently. When LDs do not efficiently use space, the
unused space consumes regions on the LD that are not available for use by the system when creating
new LDs. You can use the space management features to consolidate used space to fewer LDs, so
that unused regions are forced to one or more LDs, which are then deleted. Deleting these LDs
frees the unused space for general use by the system. You can also truncate LDs to free up space.
The used regions on the LD are compacted by moving them to the beginning of the LD, and then
the LD is shortened so that unused space can be returned to the system’s free chunklet pool.
Reclaiming Unmapped LD Space from CPGs
CPGs provide a shared pool of LD capacity for use by all virtual volumes that draw space from
that pool. See “Virtual Volume Types” (page 44) for a discussion of volumes that can draw space
from a CPG. If volumes that draw from a CPG are deleted, or if copy space for these volumes
grows and then shrinks, the underlying LDs in the CPG pool can become less efficient in space
usage. The LDs in the CPG pool may have only a small portion of their regions mapped to existing
virtual volumes. However, the unused regions on the LDs are not available for use by the volumes
mapped to the CPG. Compacting the LD regions mapped to these volumes may recover and free
LD space.
Compacting a CPG allows you to reclaim space from a CPG that has become less efficient in
space usage from creating, deleting, and relocating volumes. Compacting consolidates LD space
in CPGs in as few LDs as possible. Compacting CPGs can be performed with the HP 3PAR CLI
and the HP 3PAR Management Console. See the HP 3PAR Command Line Interface Administrator’s
Manual and the HP 3PAR Management Console Online Help for instructions on performing this
task.
52 Reclaiming Unused Space