IBM DS8000 manual Disk path redundancy, Switched disk connections

CUIR allows the DS8000 to request that all attached system images set all paths required for a particular service action to the offline state. System images with the appropriate level of software support will respond to such requests by varying off the affected paths, and either notifying the DS8000 subsystem that the paths are offline, or that it cannot take the paths offline. CUIR reduces manual operator intervention and the possibility of human error during maintenance actions, at the same time reducing the time required for the maintenance. This is particularly useful in environments where there are many systems attached to a DS8000.

4.6 Disk subsystem

The DS8000 currently supports only RAID-5 and RAID-10. It does not support the non-RAID configuration of disks better known as JBOD (just a bunch of disks).

4.6.1 Disk path redundancy

Each DDM in the DS8000 is attached to two 20-port SAN switches. These switches are built into the disk enclosure controller cards. Figure 4-7illustrates the redundancy features of the DS8000 switched disk architecture. Each disk has two separate connections to the backplane. This allows it to be simultaneously attached to both switches. If either disk enclosure controller card is removed from the enclosure, the switch that is included in that card is also removed. However, the switch in the remaining controller card retains the ability to communicate with all the disks and both device adapters (DAs) in a pair. Equally, each DA has a path to each switch, so it also can tolerate the loss of a single path. If both paths from one DA fail, then it cannot access the switches; however, the other DA retains connection.

to next

expansion enclosure

Server 0

device adapter

Server 1

device adapter

to next

expansion enclosure

Fibre channel switch Fibre channel switch

Storage enclosureMidplane backplane

Figure 4-7 Switched disk connections

Chapter 4. RAS 75