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Important:  A prefer red practice is to use IBM Easy Tier to balance workload across all ranks even when only a single tier of drive type is installed in an extent pool. Use the Enable  option that is shown in Figure 6-5 to auto-rebalance all pools. 

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## Storage pool striping: Extent rotation 

Storage pool striping is a technique for spreading data across several disk arrays. The I/O capability of many disk drives can be used in parallel to access data on the logical volume. 

The easiest way to stripe is to create extent pools with more than one rank and use storage pool striping when you allocate a new volume. This striping method does not require any operating system support. 

The number of random I/Os that can be run for a standard workload on a rank is described in 6.3, “Performance considerations for drives” on page 159. If a volume is on only one rank, the I/O capability of this rank also applies to the volume. However, if this volume is striped across several ranks, the I/O rate to this volume can be much higher. 

The total number of I/Os that can be run on a set of ranks does not change with storage pool striping. 

Important:  Use storage pool striping and extent pools with a minimum of 4 - 8 ranks to avoid hot spots on the disk drives. Consider combining this configuration with Easy Tier auto-rebalancing. 

