IBM System Storage DS4000, Hardware Manual

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Chapter 3. IBM System Storage DS4000 and DS5000 hardware
37
In the example shown in Figure 3-11, the array is built on five enclosures and uses five disk
ports to communicate. Note that disk number 2 is placed in the second enclosure in the
second position in the enclosure, and so on (“barber pole” volume). If all drives are placed
vertically (on many enclosures), but in the same position, for example, the first slot, five disk
ports are used, but all in the same controller, using one (of two) quad disk port chips.
Figure 3-11 Data flow with more expansions
Write operation steps
Here are the write operation steps:
1. Data comes through the host port of the preferred controller for the volume.
2. Data is written to cache.
a. If cache mirroring is enabled, cache without battery is disabled, the battery state is
okay (or just cache without battery is enabled), and data is copied to the second
controller.
b. If Enhanced Remote Mirroring is established for the volume, the remote copy
procedure starts. If synchronous mode is used, data is copied to a remote DS5000.
c. If write caching is enabled, the host receives the message I/O completed.
3. Data is written to disks of the array.
4. Depending on the number of disks, the local or second controller’s ports are used for
writing.
Encl 1
Encl 2
Encl 3
Encl 4
Encl 5
Encl 6
Encl 7
Encl 8
7 6 5 4 3 2 1 8 7 6 5 4 3 2 1 8 7 6 5 4 3 2 1 8 8 7 6 5 4 3 2 1
Quad-Port
4 Gb FC
Interconnect Board
Controller A Controller B
Mirror Mirror
Host Ports Host Ports
Loop Switch
Detail
1 MB
HIC HIC HIC HIC
1 MB
.256
KB
(2,4
)
.256K
B (1,3,p
)
.256KB
(1)
7 6 5 4 3 2 1 8 7 6 5 4 3 2 1 8 7 6 5 4 3 2 1 8 8 7 6 5 4 3 2 1
Quad-Port
4 GB FC
Quad-Port
4 GB FC
Quad-Port
4 GB FC
Quad-Port
4 GB FC
Data Layout
4 Enclosure 4
3 Enclosure 3
2 Enclosure 2
1 Enclosure 1
P Enclosure 5
.256KB
(3)
.256KB
(P)
.256KB (2)
.256KB (4)
Quad-Port
4 Gb FC
Quad-Port
4 GB FC
Loop
Switch
Loop
Switch
Loop
Switch
1,3,p 1
Loop
Switch
3 P
Quad-Port
4 Gb FC
Quad-Port
4 GB FC
Loop
Switch
Loop
Switch
Loop
Switch
2
Loop
Switch
Loop
Switch
4
Quad-Port
4 Gb FC
Quad-Port
4 Gb FC
Quad-Port
4 GB FC
Quad-Port
4 GB FC
Zip
Zip
Processor
Zip Zip
Processor
Note: Normally, when both controllers are running, disk loop ports in controller A access
odd drives in a disk enclosure. Disk loop ports in controller B access even drives in a disk
enclosure. Each controller has connections to all disk ports in both controllers. When the
controller fails, the running one uses its ports to communicate to all drives.