8456ch_Perf.fm Draft Document for Review December 11, 2019 12:14 pm 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. 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.  Figure 6-5 Easy Tier option to auto-balance all extent pools Storage pool striping: Extent rotation 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. 168  IBM DS8900F Architecture and Implementation