Rules For Ssa Loops; Loops And Data Paths - IBM F80 Service Manual

identification that is related to the position of the disk drive-module in the SSA string.
After configuration, the disk drive module always has the same identification. It can be
moved to any position on the SSA link, but can always be found by the software.
Service actions are always related to physical disk drives. For this reason, errors that
occur on SSA disk drives are always logged against the physical disk drive (pdisk).
The numeric identifier of pdisks, hdisks, and disk drive module slots of the system unit
are not related to each other. For example, pdisk1 is not necessarily installed in slot 1
of the six-pack.
The disk drive module serial number, on the label on the front of the carrier, is also
displayed by the service aids. It is the last eight digits of the drive's IEEE SSA unique
ID, which is stored on the drive's electronics card.

Rules for SSA Loops

The following are rules for SSA loops:
v The SSA loop must be connected to the internal pair of connectors on the SSA
adapter.
v Only one pair of adapter connectors can be connected to a particular SSA loop.
v A maximum of 18 disk drive modules can be connected in a particular SSA loop.
v A maximum of three dummy disk drive modules can be connected next to each other
in a particular SSA loop.

Loops and Data Paths

All devices that are attached to an SSA adapter card are connected through SSA links.
The SSA links are configured as loops. Data and commands to a particular device pass
through all other devices on the link between the adapter and the target device.
Data can travel in either direction around a loop. The adapter can, therefore, access the
disk drive modules through two data paths. The using system cannot detect which data
path is being used.
If a disk drive module fails or is turned off, the loop is broken and one of the data paths
to a particular module is no longer available. The disk drive modules on the loop
continue to work, but an error is reported to the using system.
The following diagram shows that the disk drive module in slot 3 has failed. The disk
drive modules in slots 1 and 2 can communicate with the using system only through
connector A1 of the SSA adapter. The disk drive modules in slots 4, 5, and 6 can
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