8456ch_Virtualization_Concepts.fm Draft Document for Review December 5, 2019 4:33 pm Extent pools can be expanded by adding more ranks to the pool. All ranks that belong to  extent pools with the same internal server affinity are called a  rank group . Ranks are  organized in two rank groups. Rank group 0 is controlled by server 0, and rank group 1 is  controlled by server 1. 4.4.1 Dynamic extent pool merge Dynamic extent pool merge  is a capability that is provided by the Easy Tier manual mode  facility, illustrated in Figure 4-4. It allows one extent pool to be merged into another extent pool  if they meet these criteria: The logical volumes in both extent pools remain accessible to the host systems. Dynamic  extent pool merge can be used for the following reasons: GLYPH<SM590000> Have extents of the same size  GLYPH<SM590000> Have the same storage type (FB or CKD) GLYPH<SM590000> Have the same DS8900F internal server affinity GLYPH<SM590000> Consolidation of two smaller extent pools with the equivalent storage type (FB or CKD)  and extent size into a larger extent pool. Creating a larger extent pool allows logical  volumes to be distributed over a greater number of ranks, which improves overall  performance in the presence of skewed workloads. Newly created volumes in the merged  extent pool allocate capacity as specified by the selected extent allocation algorithm.  Logical volumes that existed in either the source or the target extent pool can be  redistributed over the set of ranks in the merged extent pool by using the Migrate Volume  function.  GLYPH<SM590000> Consolidating extent pools with different storage tiers to create a merged extent pool with  a mix of storage drive technologies. This type of an extent pool is called a  multi-tiered pool and is a prerequisite for using the Easy Tier automatic mode feature. 106  IBM DS8900F Architecture and Implementation Figure 4-4 Easy Tier migration types Easy Tier Application • Application-assisted data  placement to designated tiers. Merged Tier 0 Pools Tier 1 Pools Tier 2 Pools Merge Pools Manual Volume Migration • Change Disk Class • Change RAID Type • Change striping Easy Tier Application Volume based data relocation Cross tier data relocation Automated intra tier data relocation