IBM Midrange System DS4000 Series Hardware Manual page 55

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.
Controller A
Mirror
Quad -Port Quad-Port
4 GB FC
4 Gb FC
Zip
Zip
Processor
Quad -Port Quad-Port
4 GB FC
4 Gb FC
1 MB
HIC HIC
Quad-Port Quad-Port
4 GB FC 4 GB FC
8 8 7 7 6 6 5 5 4 4 3 3 2 2 1 1
Host Ports
Data Layout
1 Enclosure 1
2 Enclosure 2
1 MB
3 Enclosure 3
4 Enclosure 4
P Enclosure 5
Figure 3-11 Data flow with more expansions
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.
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.
Interconnect Board
Loop Loop Loop Loop
1 1,3,p 3 P
Switch Switch Switch
Switch
8 8 7 7 6 6 5 5 4 4 3 3 2 2 1 1
Encl 1
.256KB
(1)
Encl 3
.256KB
(3)
Encl 5
.256KB
(P)
Encl 7
Chapter 3. IBM System Storage DS4000 and DS5000 hardware
Loop Loop
Loop Loop Loop
2 4
Switch Switch Switch Switch Switch
1 1 2 2 3 3 4 4 5 5 6 6 7 7
Encl 2
.256KB (2)
Encl 4
.256KB (4)
Encl 6
Encl 8
Controller B
Mirror
Quad-Port Quad -Port
4 GB FC
4 Gb FC
Zip Zip
Processor
Quad-Port Quad -Port
4 GB FC
4 Gb FC
HIC HIC
Quad-Port Quad-Port
Quad -Port
4 GB FC
4 GB FC 4 Gb FC
8 8 1 1 2 2 3 3 4 4 5 5 6 6 7 7 8 8
Host Ports
Loop Switch
Detail
37