120 DS8800 Performance Monitoring and Tuning
match the number of ranks (or be at least a multiple of this number). Otherwise, the result is
an imbalanced volume and workload distribution across the ranks and likely rank bottlenecks.
However, efficient host-based striping must be guaranteed in this case to spread the workload
evenly across all ranks, eventually from two or more extent pools. See 3.2.7, “Extent
allocation methods (EAMs)” on page 68 for more details about the EAMs and how the volume
data is spread across the ranks in an extent pool.
Even multi-rank extent pools provide some level of control of volume placement across the
ranks in cases where it is necessary to manually enforce a special volume allocation scheme.
You can use the ...