SimpleTech ZeusIOPS - Manual (Page 54)

54 Zeus IOPS 3.5-Inch Fibre Channel Solid State Drive Product Manual Rev. 1.0
An Arbitrated Loop has certain rules:
1 Each 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.
2 The 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.
3 There 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.
4 If 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.
5 The 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.