3PAR InForm® OS 2.3.1 Concepts Guide (320-200112 Rev B, February 2010)

11.2
Reclaiming Unmapped Logical Disk Space from CPGs
3PAR InForm OS Concepts Guide InForm OS Version 2.3.1
Mapping is the correspondence of Logical Disk (LD) regions to the virtual volume regions.
Virtual volumes are made up of multiple logical disks, and each logical disk contains regions
that are mapped to the virtual volume. All types of volumes are created by mapping data from
one or more logical disks to the virtual volume. Figure 11-1 shows how data mapped in regions
from logical disks onto a base volume.
Figure 11-1. Data is mapped from logical disks onto a virtual volume in regions
Logical disks can be shared by multiple virtual volumes. As volumes are deleted or as volume
copy space grows and then shrinks, logical disks can use space less efficiently. When logical
disks 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 logical disks. The space management
features enable you to consolidate used space onto fewer fully-used logical disks so that
unused regions are forced onto one or more logical disks that are then deleted. Deleting these
logical disks frees the unused space for general use by the system. You can also truncate LDs to
free up space. The LD’s used regions 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.
11.2 Reclaiming Unmapped Logical Disk Space from CPGs
Common Provisioning Groups (CPGs) provide a shared pool of logical disk capacity for use by
all virtual volumes that draw space from that pool. See Virtual Volume Types on page 10.2 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 logical disks
in the CPG pool can become less efficient in space usage. One or more logical disks in the CPG
AA
DD
BB
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CC
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A
P (E,F)
B
E
P (A,B)
F
C
P (G,H)
D
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P (C,D)
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Region
Logical disk (RAID 5)
Virtual volume
Region
Logical disk (RAID 1)
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RAID set
LD
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Chunklet
Mirror
LD
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