IBM DS6000 Series manual Minimize the number of extent pools, 239

Minimize the number of extent pools

The other extreme is to create just two extent pools when the DS6000 is configured as CKD storage only. You would then subdivide the disk subsystem evenly between both processor complexes or servers as Figure 11-13shows.

	preferred path		preferred path
blue I/O	red I/O		blue I/O	red I/O
	Server 0		Server 1
	blue		red
Rank	1	3	2	4
	5	7	6	8
	9	11	10	12
	Extent pool0		Extent pool1

Figure 11-13 Extent pool affinity to processor complex with pooled ranks in two extent pools

Again what is obvious here is the affinity between all volumes residing in extent pool 0 to the left processor complex, server 0, including its HA, and the same for the volumes residing in extent pool 1 and their affinity to the right processor complex or server 1.

When creating volumes there is no straightforward approach to place certain volumes into certain ranks. For example, when you create the first 20 DB2 logging volumes, they would be allocated in a consecutive fashion in the first rank. The concerned RAID site would then host all these 20 logging volumes. You may have the desire to control the placement of the most critical performance volumes and also configure for preferred paths. This might lead to a compromise between both approaches, as Figure 11-14 on page 240 suggests.

Plan for a reasonable number of extent pools

Figure 11-14presents a grouping of ranks into extent pools which follows a similar pattern and discussion as for grouping volumes or volume pools into SMS storage groups.

Chapter 11. Performance considerations 239