IBM DS6000 Series manual Raw or physical DDM layer, Array site layer, Array layer, Rank layer

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.

Chunk1

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Parity

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Chunk7

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Parity	Spare
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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.

162DS6000 Series: Concepts and Architecture