IBM totalstorage fastt100, Installation, User And Maintenance Manual, Page: 60 / 160

Each drive enclosure in a FAStT storage subsystem drive loop must have a unique
drive enclosure ID. FAStT controllers use a combination of the enclosure ID and the
number of the physical slot that a fibre channel hard drive occupies to create a
unique fibre channel loop address or arbitrated loop physical address (AL_PA) for
each drive in a fibre channel drive loop. The enclosure ID consists of two digits, a
tens digit (x10) and ones digit (x1).
Attention: When connecting the FAStT100 to EXP100 drive enclosures, DO NOT
use the tens digit (x10) setting. Use only the ones digit (x1) setting to set unique
server IDs or enclosure IDs.
Give each drive expansion enclosure in a redundant drive loop a unique ones digit
(x1) ID. This setting will enforce hard AL_PAs (unchangeable between fibre channel
Loop Initializations [LIPs]) for the drives and facilitate drive loop problem
troubleshooting in the event of an error. If the ones digits are not unique, two or
more devices will have the same hard AL_PA. In such a case, the controller will use
soft AL_PAs for the devices that have identical hard AL_PAs.
The problem with soft addressing is that addresses may change between LIPs. This
possibility increases the difficulty of troubleshooting drive loop problems, since one
cannot easily ascertain whether the same device with a different address or
different device may be causing a problem.
Note: The FAStT100 is shipped with 00 as the default server ID setting. If you
connect the storage server to a FAStT EXP100, you must set the EXP100
enclosure ID setting to a value other than 00. Each server unit should have a
unique ID if it is going to be connected to other drive expansion units
through the drive loop ports. The Server ID setting is only valid for the drive
Server ID Switch
f10ug062
Figure 21. Setting the Server ID
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IBM TotalStorage FAStT100 Storage Server: Installation, User’s, and Maintenance Guide