IBM System storage DS6000 Series, Redbooks

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Chapter 8. Configuration planning
141
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).
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.
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.
FB RAID rank capacity
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
Rank
RAID
type DDM
capacity Array
format
Extents
Binary
GB Decimal
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