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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.
UsingSystem1
A1 A2 B1 B2 A1 A2 B1 B2
Disk
1
Disk
2
Disk
3
Disk
4
Disk
5
Disk
6
Disk
7
Disk
8
Disk
12
Disk
11
Disk
10
Disk
9
Disk
16
Disk
15
Disk
14
Disk
13
1
2
UsingSystem2
B2 B1 A2 A1 B2 B1 A2 A1
3
4
Figure 7. Disk Drives Isolated by Failing Using System
Chapter 2. Introducing SSA Loops 13