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162 DS6000 Series: Concepts and Architecture
Raw or physical DDM layer
At the very top, you can see the raw DDMs. There are four DDMs in a group called a
four-pack. They are placed into the DS6000 in pairs of two, making eight DDMs. DDM X
represents one four-pack and DDM Y represents a pair from another four-pack. Upon placing
the four or eight-packs into the DS6000 each four or eight-pack is grouped into array sites,
shown as Layer 2. The DS6000 does support 4 DDM arrays; this is not described here.
Array site layer
At the array site level, predetermined groups of four DDMs of the same speed and capacity
are arranged. All DDMs reside in the same Disk Enclosure (Array On Loop configuration).
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 9-8. 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 choose 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.
Figure 9-8 Diagram of how parity is striped across physical disks
Rank layer
At this level the ranks are formed. Presently only one array can make up a rank, as shown in
Figure 9-7 on page 161.
Extent pool layer
At this level the extent pools are formed. In Figure 9-7 on page 161 we show that extent pool
A is made up of 2 ranks, rank 1 and rank 2. The extents in the pool are 1 GB.
Logical volume layer
Layer 6 is the final level of the LUN formation. We show in Figure 9-7 on page 161 that two
LUNs were created out of extent pool A. The top LUN is made up of 12 extents, making it a
12GB LUN. The bottom LUN is made up of 24 extents, making it a 24GB LUN.
Logical Configuration flow
Figure 9-9 on page 163 shows the recommended flow for performing logical configuration
using the GUI.
Spare
Chunk1
Chunk2
Chunk3
Chunk4
Chunk5
Chunk6
Parity
Chunk1
Chunk2
Chunk3
Chunk4
Chunk5
Parity
Chunk7
Chunk1
Chunk2
Chunk3
Chunk4
Parity
Chunk6
Chunk7
Chunk1
Chunk2
Chunk3
Parity
Chunk5
Chunk6
Chunk7
Chunk1
Chunk2
Parity
Chunk4
Chunk5
Chunk6
Chunk7
Chunk1
Paity
Chunk3
Chunk4
Chunk5
Chunk6
Chunk7
Parity
Chunk2
Chunk3
Chunk4
Chunk5
Chunk6
Chunk7