control the placement of each single volume and where it ends up in the disk subsystem. For the DS6000 this would have the advantage that you can plan for proper volume placement with respect to preferred paths.
In the example in Figure
Now all volumes which are comprised of extents out of an extent pool have also a respective server affinity when scheduling I/Os to these volumes.
This allows you to place certain volumes in specific ranks to avoid potential clustering of many high activity volumes within the same rank. You can create SMS storage groups which are congruent to these extent pools to ease the management effort of such a configuration. But you can still assign multiple storage groups when you are not concerned about the placement of less active volumes.
blue I/O
preferred path | preferred path |
red I/O | blue I/O |
red I/O
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Figure 11-12 Extent pool affinity to processor complex with one extent pool for each rank
Figure 11-12 indicates that there is an affinity between FICON ports and certain extent pools and, therefore, an affinity between FICON ports and certain volumes within these extent pools.
In this example either one of the two HAs can address any volume in any of the ranks. which range here from rank number 1 to 12. But the HA and DA affinity to a server prefers one path over the other. Now z/OS is able to notice the preferred path and then schedule an I/O over the preferred path as long as the path is not saturated.
238DS6000 Series: Concepts and Architecture
