IBM H Series Installation And Service Manual page 211

The SSA links must be configured as loops. The loop is connected to the internal
connectors at the SSA adapter card. These connectors must be a valid pair (that is,
A1 and A2, or B1 and B2); otherwise, the disk drive modules on the loop are not fully
configured, and the diagnostics fail. Operations to all the disk drive modules on a
particular loop can continue if that loop breaks at any one point.
Each pair of connectors has a green light that indicates the operational status of its
related loop:
Status of Light Meaning
Off Both SSA connectors are inactive. If disk drive modules are connected to
these connectors, either those modules are failing, or their SSA links have not
been enabled.
Permanently on Both SSA links are active (normal operating condition).
Slow flash Only one SSA link is active.
Disk Drive Module Strings
In the system unit, the disk drive modules are arranged in a string of two to six disk
drive modules. This string has its own two SSA connectors. This string is connected
through an internal SSA cable to a pair of connectors on the SSA adapter to make
an SSA loop. (The SSA cables provide the SSA links.)
The following diagram shows the relationships between the SSA connectors and the
disk drive module string in a system unit.
Chapter 5. SSA Software and Microcode Errors
5-15