Preventing the Isolation of Disk Drives in Higher-Availability Configurations
If a loop contains four SSA attachments, with two attachments in each of two using
systems, disk drive modules become isolated if they are connected between the two
SSA attachments of one using system, and both those attachments fail, or are held
reset, but remain powered on.
Bypass Note: A bypass card switches the internal strings of the 7133 only if it detects
that neither of its connectors is connected to a powered-on SSA
attachment or device. Therefore, if the two SSA attachments fail, or are
held reset, but remain powered on, the bypass card does not operate,
and the disk drive modules become isolated.
In Figure 34, SSA attachments
1
and
2
are in using system 1; SSA attachments
3
and
4
are in using system 2. In each using system, the two SSA attachments are
connected to each other.
If the two SSA attachments of either using system fail, or are held reset, but remain
powered on, all the disk drive modules can still communicate with the other using
system.
Using System 1
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
Using System 2
B2 B1
A2 A1
B2 B1
A2 A1
3
4
Figure 34. One Loop, Two SSA Attachments in Each of Two Using Systems
Chapter 1. Reference Information
57
Summary of Contents for 7133 D40
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