The number of arrays that are required in terms of performance must be defined in the  pre-sales or solution design phase. However, when sizing the environment keep in mind that  adding too many arrays to a single storage pool increases the failure domain, and therefore it  is important to find the trade-off between the performance, availability, and scalability cost of  the solution. The following actions are the starting preferred practices when planning storage pools for  performance: Limitation:  Image Mode volumes are not supported with Data Reduction Pools. Limitation:  Child pools (VVols) are not supported with Data Reduction Pools When adding MDisks to a pool they are logically divided into chunks of equal size. These  chunks are called  extents  and are indexed internally. Extent sizes can be 16, 32, 64, 128, 256,  512, 1024, 2048, 4096, or 8192 MB. The IBM Spectrum Virtualize architecture can manages  2^22 extents for a system and therefore the choice of extent size affects the total amount of  storage that can be addressed. Check the  link  for the capacity limits per extent size. When planning for the extent size of a pool, remember that you cannot change the extent size  later, it must remain constant throughout the lifetime of the pool. For the pool extent size planning, consider the following recommendations: GLYPH<SM590000> Create a dedicated storage pool with dedicated resources if there is a specific  performance application request.  GLYPH<SM590000> In a IBM FlashSystem 9100 clustered environment, create storage pools with IOgrp or  Control Enclosure affinity. That means you have to use only arrays/MDisks supplied by the  internal storage that is directly connected to one IOgrp SAS chain only. This configuration  avoids unnecessary IOgrp-to-IOgrp communication traversing the SAN and consuming  Fibre Channel bandwidth. GLYPH<SM590000> Use dedicated pools for image mode volumes. GLYPH<SM590000> Try to limit the number of storage pools to avoid excessive cache partitioning. GLYPH<SM590000> For those Easy Tier enabled storage pools, always allow some free capacity for Easy Tier  to deliver better performance. GLYPH<SM590000> Consider implementing child pools when you need to have a logical division of your  volumes for each application set. There are often cases where you want to subdivide a  storage pool but maintain a larger number of MDisks in that pool. Child pools are logically  similar to storage pools, but allow you to specify one or more subdivided child pools.  Thresholds and throttles can be set independently per child pool.  GLYPH<SM590000> For standard pools usually 1 GB is suitable GLYPH<SM590000> For Data Reduction Pools use 4 GB (see 4.7, “Data Reduction Pools Best Practices” on  page 93 for further considerations on extent size for DRP) GLYPH<SM590000> With Easy Tier enabled hybrid pools, consider smaller extent sizes to better utilize the  higher tier resources and therefore provide better performance. GLYPH<SM590000> Keep the same extent size for all pools if possible. The extent based migration function is  not supported between pools with different extent sizes. However, you can use volume  mirroring to create copies between storage pools with different extent sizes. 4.3.3 Extent size considerations Chapter 4. Storage Pools  73