IBM DS8000 manual 179, Sparing example 3 RAID-5 Different capacity, same RPM

Sparing Example 3 – RAID-5:

1st 4 arrays 146GB & next 2 arrays 300GB (same RPM)

	6 + P	6 + P	6 + P		6 + P	6 + P	6 + P
	Array	Array	Array		Array	Array	Array
DA	1		5	…		4	DA
		3		…	6		2
	146GB	146GB	300GB		300GB	146GB	146GB

•Assumes all devices same RPM

•Minimum of 4 spares per DA pair

–2 spares per loop & 2 spares in each array group

–Additional 146GB RAID arrays will be 7 + P (RAID-5) or 4x2 (RAID-10)

•Minimum 4 spares of the largest capacity array site on the DA pair

–Next 2 300GB arrays will also be 6 + P (if RAID-5)

•If next 300GB array configured is RAID-10, then that array will be 3x2 and any additional 300GB arrays on this DA pair will not have spares

•All spares available to all arrays on the DA pair

Figure 9-11 Sparing example 3: RAID-5 - Different capacity, same RPM

Figure 9-11illustrates an intermix configuration in a DA pair.

1.At first, four RAID-5 arrays with 146 GB DDMs are installed in a DA pair. Each array needs a spare disk drive (6+P+S). Two spare disks are in one loop and other two spare disks are in the other loop in the DA pairs.

2.Next, two RAID-5 arrays with 300 GB DDMs are added in the DA pair. According to the rule of Minimum 4 spare disks of the largest capacity array site on the DA pair, an additional 2 arrays need a spare disk (6+P+S).

3.If you add other arrays with 300 GB DDMs, you need spare disks in additional arrays. You need a total of four 300 GB spare disks in the DA pair; then, two 6+P+S arrays are needed for RAID-5, and one 3x2+2S array is needed for RAID-10.

Note: Intermix of DDM size and RPM configuration is planned for the future.

Chapter 9. Configuration planning 179