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Chapter 4. RAS 75
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 4-7 illustrates 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.
Figure 4-7 Switched disk connections
Midplane
to next
expansion
enclosure
Server 1
device adapter
Server 0
device adapter
Fibre channel switch
Storage enclosure backplane
Fibre channel switch
to next
expansion
enclosure