Preventing The Isolation Of Disk Drives In Higher-Availability Configurations - IBM 7133 D40 Service Manual

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
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.
Disk
Disk
Figure 34. One Loop, Two SSA Attachments in Each of Two Using Systems
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.
Using System 1
A1 A2 B1 B2
1
Disk Disk Disk
16 15 14 13
Disk Disk Disk
1 2 3
3
B2 B1 A2 A1
Using System 2
2
A1 A2
Disk Disk
12 11
Disk Disk
4 5 6
4
B2 B1
Chapter 1. Reference Information
B1 B2
Disk Disk
10 9
Disk Disk
7 8
A2 A1
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