IBM DS8000 manual Sparing rules, FB RAID rank capacity

FB RAID rank capacity

	Spare /		Binary	Decimal
Rank	No spare	Extents	GB	GB
RAID10 73GB	Spare	192	192	206.16
RAID10 73GB	No spare	256	256	274.88
RAID10 146GB	Spare	386	386	414.46
RAID10 146GB	No spare	519	519	557.27
RAID10 300GB	Spare	785	785	842.89
RAID10 300GB	No spare	1,048	1,048	1,125.28
RAID5 73GB	Spare	386	386	414.46
RAID5 73GB	No spare	450	450	483.18
RAID5 146GB	Spare	779	779	836.44
RAID5 146GB	No spare	909	909	976.03
RAID5 300GB	Spare	1,582	1,582	1,698.66
RAID5 300GB	No spare	1,844	1,844	1,979.98

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 9-8 FB RAID rank capacity

For example, if you configure a RAID-5 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 DS8000, extent size is specified with binary size, not decimal size. For example, 1 GB in binary is described as 1024 x 1024 x 1024, and 1GB in decimal is described as 1000 x 1000 x 1000. Operating systems adopt the binary format for calculating their storage.

9.4.2 Sparing rules

To estimate your usable storage capacity, it is helpful to understand the rules of sparing since the capacity of the rank is different with or without spare disks in the rank. The sparing rules for the DS8000 are as follows:

￿A minimum of one spare is required for each array site defined until the following considerations are met:

–Minimum of 4 spares per DA pair.

The spares are balanced between the two device interfaces.

–Minimum of 4 spares per the largest capacity array site on the DA pair. The spares are balanced between the two device interfaces.

–Minimum 2 spares of capacity and RPM greater than or equal to the fastest array site of any given capacity on the DA pair.

The spares are balanced between the two device interfaces.

￿Spares are not necessarily allocated on the first arrays to be formatted.

￿Intermix configuration complicates the sparing rules. You should use Capacity Magic for these calculations.

176DS8000 Series: Concepts and Architecture