IBM Advanced SerialRAID Adapters SA33-3285-02 User Manual page 33

If, however, disk drives are connected into the link between two SSA adapters that are
in the same using system, those disk drives become isolated if both SSA adapters fail,
or are held reset, but remain powered on (see also "Bypass Note" on page 12). In
Figure 7, disk drives 13 through 16 have been connected between the SSA adapters in
using system 1. If both adapters fail, or are held reset, but remain powered on, disk
drives 1 through 12 can still communicate with using system 2. Disk drives 13 through
16, however, cannot communicate with using system 2, because their data paths are
through the adapters in using system 1. When using system 1 is rebooted, disk drives
13 through 16 remain unavailable for a long time.
A1 A2 1 B1 B2
Disk Disk Disk
16 15 14
Disk Disk Disk
1 2 3
3
B2 B1 A2 A1
Figure 7. Disk Drives Isolated by Failing Using System
Using System 1
A1 A2
Disk
13
Disk Disk
12 11
Disk Disk Disk
4 5 6
B2 B1
Using System 2
Chapter 2. Introducing SSA Loops
2
B1 B2
Disk Disk
10 9
Disk Disk
7 8
4
A2 A1
13