The DS8000 series controllers assign server (controller) affinity to ranks when they are added  to an extent pool. Ranks that belong to an even-numbered extent pool have an affinity to  server0, and ranks that belong to an odd-numbered extent pool have an affinity to server1. Figure 2-4 shows an example of a configuration that results in a 50% reduction in available  bandwidth. Notice how arrays on each of the DA pairs are accessed only by one of the  adapters. In this case, all ranks on DA pair 0 are added to even-numbered extent pools, which  means that they all have an affinity to server0. Therefore, the adapter in server1 is sitting idle.  Because this condition is true for all four DA pairs, only half of the adapters are actively  performing work. This condition can also occur on a subset of the configured DA pairs. Example 2-6 shows what this invalid configuration looks like from the CLI output of the  lsarray  and  lsrank  commands. The arrays that are on the same DA pair contain the same  group number (0 or 1), meaning that they have affinity to the same DS8000 series server.  Here, server0 is represented by group0, and server1 is represented by group1.  As an example of this situation, consider arrays A0 and A4, which are attached to DA pair 0.  In this example, both arrays are added to an even-numbered extent pool (P0 and P4) so that  both ranks have affinity to server0 (represented by group0), which leaves the DA in server1  idle. Figure 2-4 DA pair reduced bandwidth configuration Example 2-6 Command output for the lsarray and lsrank commands Chapter 2. Back-end storage  63 dscli> lsarray -l Date/Time: Oct 20, 2016 12:20:23 AM CEST IBM DSCLI Version: 7.8.1.62 DS: IBM.2107-75L2321 Array State Data RAID type arsite Rank DA Pair DDMcap(10^9B) diskclass =================================================================================== A0 Assign Normal 5 (6+P+S) S1 R0 0 146.0 ENT A1 Assign Normal 5 (6+P+S) S9 R1 1 146.0 ENT A2 Assign Normal 5 (6+P+S) S17 R2 2 146.0 ENT A3 Assign Normal 5 (6+P+S) S25 R3 3 146.0 ENT A4 Assign Normal 5 (6+P+S) S2 R4 0 146.0 ENT A5 Assign Normal 5 (6+P+S) S10 R5 1 146.0 ENT A6 Assign Normal 5 (6+P+S) S18 R6 2 146.0 ENT