30 Implementing the IBM Storwize V7000 with IBM Spectrum Virtualize V8.2.1
2.5.15  Storage pool
A storage pool is a collection of MDisks that are grouped to provide capacity for volumes. All 
MDisks in the pool are split into extents with 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 storage 
pool. MDisks can belong in only one storage pool, and only MDisks in unmanaged mode can 
be added to the storage pool. When an MDisk is added to the storage pool, the mode 
changes from unmanaged to managed (and vice versa when you remove it).
Each MDisk in the storage pool is divided into several extents. The size of the extent is 
selected by the administrator at creation time of the storage pool, and cannot be changed 
later. The size of the extent ranges from 16 MB - 8 GB. The default extent size in V8.1 is 
1024 MB.
The extent size directly affects the maximum volume size and storage capacity of the 
clustered system. A system can manage 4 million (4 x 1024 x 1024) extents. For example, a 
system with a 16 MB extent size can manage up to 16 MB x 4 MB = 64 TB of storage.
Use the same extent size for all storage pools in a clustered system, which is a prerequisite 
for supporting volume migration 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.
IBM Storwize V7000 object names: The names must begin with a letter and can be a 
maximum of 63 characters. Valid characters for names are uppercase letters (A-Z), 
lowercase letters (a-z), digits (0 - 9), underscore (_), period (.), hyphen (-), and space. The 
names must not begin or end with a space.
Default extent size: The IBM Storwize V7000 GUI has a default extent size value of 
1024 MB when you define a new storage pool. This setting can only be changed by using 
the CLI.