IBM H Series Installation And Service Manual page 214

If two or more disk drive modules are turned off, fail, or are removed from the loop,
some modules might become isolated from the SSA adapter.
The following diagram shows that the disk drive modules in slots 2 and 4 have failed.
The disk drive module in slot 1 can communicate with the using system only through
connector A1 of the SSA adapter. The disk drive module in slots 5 and 6 can com-
municate with the using system only through connector A2 of the SSA adapter. The
disk drive module in slot 3 is isolated from the SSA adapter.
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RS/6000 Enterprise Server Model H Series Installation and Service Guide