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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
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.
Pdisks, Hdisks, and Disk Drive Module Identification
The physical disk drives (pdisks) in an SSA subsystem can be configured as logical
units (LUNs). A LUN is also known as an hdisk, and can consist of one or more
physical disk drives. An hdisk in an SSA subsystem might, therefore, consist of one
pdisk or several pdisks.
The configuration software also allocates an identification (hdisk and pdisk number) to
each disk drive module during the configuration of the SSA link. The disk drive modules
do not have fixed physical addresses.
The configuration software first recognizes the disk drive module by the
machine-readable serial number that is written on the disk. Then, it assigns an
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.
Appendix F. SSA Software and Microcode Errors
439
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