Chapter 1. Overview of the IBM Storwize V5000 Gen2 system 23
1.6.8 Storage pools
A storage pool (up to 1028 per system) is a collection of MDisks (up to 128) that are grouped
to provide capacity for volumes. All MDisks in the pool are split into extents of the same size.
Volumes are then allocated out of the storage pool and are mapped to a host system.
MDisks can be added to a storage pool at any time to increase the capacity of the pool.
MDisks can belong in only one storage pool. For more information, see Chapter 4, “Storage
pools” on page 143.
Each MDisk in the storage pool is divided into a number of extents. The size of the extent is
selected by the administrator when the storage pool is created and cannot be changed later.
The size of the extent ranges from 16 MB - 8 GB.
The extent size directly affects the maximum volume size and storage capacity of the
clustered system.
A system can manage 2^22 (4,194,304) extents. For example, with a 16 MB extent size, the
system can manage up to 16 MB x 4,194,304 = 64 TB of storage.
The effect of extent size on the maximum volume and cluster size is shown in Table 1-12.
Table 1-12 Maximum volume and cluster capacity by extent size
Use the same extent size for all storage pools in a clustered system. This rule is a
prerequisite if you want to migrate a volume between two storage pools. If the storage pool
extent sizes are not the same, you must use volume mirroring to copy volumes between
storage pools, as described in Chapter 4, “Storage pools” on page 143.
You can set a threshold warning for a storage pool that automatically issues a warning alert
when the used capacity of the storage pool exceeds the set limit.
Default extent size: The GUI of IBM Storwize V5000 Gen2 has a default extent size value
of 1024 MB when you define a new storage pool.
Extent size (MB) Maximum volume capacity for
normal volumes (GB)
Maximum storage capacity of
cluster
0016 002,048 (2 TB) 064 TB
0032 004,096 (4 TB) 128 TB
0064 008,192 (8 TB) 256 TB
0128 016,384 (16 TB) 512 TB
0256 032,768 (32 TB) 001 PB
0512 065,536 (64 TB) 002 PB
1024 131,072 (128 TB) 004 PB
2048 262,144 (256 TB) 0v8 PB
4096 262,144 (256 TB) 016 PB
8192 262,144 (256 TB) 032 PB
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