SimpleTech ZeusIOPS manual

An Arbitrated Loop has certain rules:

1Each port on the loop has an Arbitrated Loop Physical Address (AL-PA) that is set on the “backplane” or the board to where the device is connected. Once set, the port attached to the backplane inherits the AL-PA.

2The AL-PA must have “neutral disparity”, i.e., the number of binary 0s and 1s in the AL-PA are equal when 10-bit encoded. Out of the 127 addresses, one is reserved on the loop for the fabric switch, leaving 126 possible AL-PAs.

3There may be more than 126 ports physically attached to the on a loop, but only 126 will be functional, with the remaining unable to obtain valid addresses.

4If the AL-PA of a device is not unique on the loop, the device will not participate on the loop. The user must choose another “hard address”, i.e., an AL-PA. If a unique hard address cannot be set, the user can set the backplane to an AL-PA so that the loop will assign a “soft address” to the device.

5The lower the AL-PA, the higher priority the device has on the loop while keeping “fairness”. Fairness means that every device on the loop has a chance to own the loop once before another device owns it twice.

54 ZeusIOPS 3.5-Inch Fibre Channel Solid State Drive Product Manual Rev. 1.0