HP 3PAR StoreServ 7400 4-node HP 3PAR StoreServ Storage Concepts Guide (OS 3.1 - Page 51
Reclaiming Unused Space, Overview, Reclaiming Unmapped Logical Disk Space from CPGs
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10 Reclaiming Unused Space Overview The HP 3PAR OS space consolidation features allow you to change the way that virtual volumes are mapped to logical disks in a Common Provisioning Group (CPG). Moving virtual volume regions from one logical disk to another enables you to compact logical disks, 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 42). 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 10 (page 51) shows how data mapped in regions from logical disks onto a base volume. Figure 10 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. 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" (page 42) 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 pool may have only a small portion of their regions mapped to existing virtual volumes. However, the logical disk's unused regions are not available for use by the volumes mapped to the CPG. Compacting the logical disk regions mapped to these volumes may recover and free logical disk 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 logical disk space in CPGs into as few logical disks as possible. Compacting CPGs can be performed Overview 51