IBM DS8000 manual Stripe size, 267

Balanced implementation: LVM striping			Non-balanced implementation: LUNs across ranks
	1 rank per extent pool		More than 1 rank per extent pool
Rank 1	Extent pool 1	GB LUN 1	ExtentExtentPool Pool 5
	2		Rank 5	8GB LUN
Extent
Rank 2	Extent pool 2
1GB		LUN 2	Rank 6
			Extent
			1GB
	Extent pool 3	LUN 3	Rank 7
Rank 3
	Extent pool 4	LUN 4	Rank 8
Rank 4
	LV stripped across 4 LUNs

Figure 12-10 Spreading data across ranks

Note: The recommendation is to use host striping wherever possible to distribute the access patterns across the physical resources of the DS8000.

The stripe size

Each striped logical volume that is created by the host’s logical volume manager has a stripe size that specifies the fixed amount of data stored on each DS8000 logical volume (LUN) at one time.

Note: The stripe size has to be large enough to keep sequential data relatively close together, but not too large so as to keep the data located on a single array.

The recommended stripe sizes that should be defined using your host’s logical volume manager are in the range of 4 MB to 64 MB.

You should choose a stripe size close to 4 MB if you have a large number of applications sharing the arrays and a larger size when you have very few servers or applications sharing the arrays.

12.4.5 Determining the number of connections between the host and DS8000

When you have determined your workload requirements in terms of throughput, you have to choose the appropriate number of connections to put between your open systems and the DS8000 to sustain this throughput.

A Fibre Channel host port can sustain a maximum of 206 MB/s data transfer. As a general recommendation, you should at least have two FC connections between your hosts and your DS8000.

Chapter 12. Performance considerations 267