IBM DS6000 Series manual Sparing rules, Configuration with the same type of DDMs, 141

FB RAID rank capacity

	RAID	DDM	Array		Binary	Decimal
Rank	type	capacity	format	Extents	GB	GB
RAID10 73GB	RAID10	73GB	3+3+2S	190	190	204.01
RAID10 73GB	RAID10	73GB	4+4	254	254	272.73
RAID10 146GB	RAID10	146GB	3+3+2S	386	386	414.46
RAID10 146GB	RAID10	146GB	4+4	515	515	552.98
RAID10 300GB	RAID10	300GB	3+3+2S	787	787	845.03
RAID10 300GB	RAID10	300GB	4+4	1,050	1,050	1,127.43
RAID5 73GB	RAID5	73GB	6+P+S	382	382	410.17
RAID5 73GB	RAID5	73GB	7+P	445	445	477.82
RAID5 146GB	RAID5	146GB	6+P+S	773	773	830.00
RAID5 146GB	RAID5	146GB	7+P	902	902	968.52
RAID5 300GB	RAID5	300GB	6+P+S	1,576	1,576	1,692.22
RAID5 300GB	RAID5	300GB	7+P	1,837	1,837	1,972.46

Notes

Device sizes that are not a multiple of 1 binary GB will use additional space on the disk subsystem as the allocation unit is an extent of this size

Figure 8-9 FB RAID rank capacity (8 DDMs array)

For example, if you configure a RAID-5 8 DDM rank with 146 GB DDMs with a spare disk in open system environments, the capacity of the rank totals 779 extents (779 GB).

Note: In the DS6000 series, the extent size is expressed in binary, not decimal. For example, 1 GB in binary is calculated as 1024 x 1024 x 1024, and 1 GB in decimal is calculated as 1000 x 1000 x 1000. Operating systems adopt binary format for their storage.

8.4.3 Sparing rules

To estimate your usable storage capacity, it is helpful to understand the rule of sparing disks. We explain the sparing rules for the DS6000 as follows:

￿On a DS6000, you will have up to two spares on each loop (switched FC-AL).

￿In the base frame we will have one or two spares: one spare in 8 DDMs configuration and two spares otherwise. There may be three spares if you configure RAID-5 on 8 drives and then RAID-10 on 8 drives in the first enclosure for the loop.

￿In the first expansion frame we will have one or two spares. The first expansion frame is on the second loop.

Configuration with the same type of DDMs

For example, if you configure a DS6000 with all the same type of 32 DDMs (a server enclosure with an expansion enclosure) attached to two switched FC-AL loops, you can configure four RAID arrays of 8 drives and the DS6000 will automatically assign four spare disks (two spare disks for each loop). After that, if you add more expansion enclosures, you can configure RAID arrays and the DS6000 will not assign spare disks.

Chapter 8. Configuration planning 141