IBM RS6000 Service Guide - Page 132

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 Off Permanently on Slow Flash Meaning 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. Both SSA links are active (normal operating condition). Only one SSA link is active. Disk Drive Module Strings In the system unit, the disk drive modules are arranged in a string of 2 to 6 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.) Figure 3-2 shows the relationships between the SSA connectors and the disk drive module string in a system unit. Figure 3-2. A String of Disk Drive Modules 3-60 Service Guide