66 Implementing the IBM Storwize V7000 with IBM Spectrum Virtualize V8.2.1
The Storwize V7000 supports extent sizes from 16 mebibytes (MiB) to 8192 MiB. The extent 
size is a property of the storage pool and is set when the storage pool is created. 
The extent size of a storage pool cannot be changed. If you need to change extent size, the 
storage pool must be deleted and a new storage pool configured. 
Table 3-2 lists all of the available extent sizes in a Storwize V7000 and the maximum 
managed storage capacity for each extent size.
Table 3-2   Extent size and total storage capacities per system
When planning storage pool layout, consider the following aspects: 
/SM590000Pool extent size:
– Generally, use 128 MiB or 256 MiB. The IBM Storage Performance Council (SPC) 
benchmarks use a 256 MiB extent. 
– Pick the extent size and then use that size for all storage pools.
– You cannot migrate volumes between storage pools with different extent sizes. 
However, you can use volume mirroring to create copies between storage pools with 
different extent sizes.
/SM590000Storage pool reliability, availability, and serviceability (RAS) considerations:
– The number and size of storage pools affe cts system availability. The use of larger 
number of smaller pools reduces the failure domain in case one of pools goes offline. 
However, increased number of storage pools introduces management overhead, 
effects storage space use efficiency, and is subject to the configuration maximum limit.
– An alternative approach is to create few la rge storage pools. All MDisks that constitute 
each of the pools should have the same performance characteristics.
– The storage pool goes offline if an MDisk is unavailable, even if the MDisk has no data 
on it. Do not put MDisks into a storage pool until they are needed.
– Put image mode volumes in a dedicated storage pool or pools.
/SM590000Storage pool performance considerations:
– It might make sense to create multiple storage pools if you are attempting to isolate 
workloads to separate disk drives. 
Extent size (MiB) Total storage capacity manageable per system
0016 64 tebibytes (TiB)
0032 128 TiB
0064 256 TiB
0128 512 TiB
0256 1 pebibytes (PiB)
0512 2 PiB
1024 4 PiB
2048 8 PiB
4096 16 PiB
8192 32 PiB