200 DS8000 Series: Concepts and Architecture
Figure 10-7 View of the raw DDM to LUN relationship
Raw or physical DDM layer
At the very top of Figure 10-7 you can see the raw DDMs. There are 16 DDMs in a disk drive
set. DDM X represents one 16-pack and DDM Y represents another 16-pack. Upon placing
the 16-packs into the DS8000, each 16-pack is grouped into array sites, shown as the second
layer.
Array site layer
At the array site level, predetermined groups of eight DDMs of the same speed and capacity
are arranged. An
arrays across loop strategy is used in the predetermined groupings so that
an array does not consist of the same, eight physical raw disks in the disk drive set.
Array layer
This level is where the format is placed on the array. Sparing rules are enforced depending on
which RAID format is chosen. If you choose RAID-5, then one spare is created and a RAID-5
format is striped across the remaining 7 drives. You must calculate the equivalent of one disk
that is used for parity out of the array. Although parity is not placed on one physical disk, but
striped across all the remaining disks, that parity equals one disk’s worth of capacity. See
Figure 10-8 on page 201. In this figure the RAID format is a 6 + P + S. If you add up the parity
chunks it equals one disk’s worth of capacity. If you chose RAID-10 then you would have two
spares with no parity and a 3 X 3 + 2(spares) configuration. This would continue for each
RAID array until the sparing rules are met.
6
Array Site X
DDM 16-pack X
Rank1
Array Site Y
Volumes/LUNs
Host
Array X
(Extent Pool A)
Each extent = 1
GB
CKD or FB
Array Y
RAID5 or RAID10
DDM 16-pack Y
RAID5 or RAID10
Rank2
Virtualization Layers Hierarchy
Raw DDM layer
array site layer
array layer
rank layer
extent pool layer
Volume layer
