SSA RAID Adapter Installation and User's Guide.
Loops and Data Paths
C.1.1.1 Loops and Data Paths
All devices that are attached to an SSA adapter card 1 are connected through SSA links 2 . The SSA links are configured in 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 round a loop. The adapter can, therefore, get access to the devices 3 (disk drives in this example) through two data paths. The system cannot detect which data path is being used.
If a disk drive fails, or is turned off, the loop is broken, and one of the data paths to a particular disk drive is no longer available. The disk drives on the remains of the loop continue to work, but an error is reported to the system.
In the diagram, disk drive number 3 has failed. Disk drives 1 and 2 can communicate with the system only through connector A1 of the SSA adapter. Disk drives 4 through 8 can communicate only through connector A2 of the SSA adapter.
_ Copyright IBM Corp. 1996
C.1.1.1 - 1
