IBM System Storage Subsystem DS5020 - Manual (Page 108)

Storage expansion enclosure settings
This section provides information about storage expansion enclosure settings. For
additional detail, refer to the Installation, User’s, and Maintenance Guide for your
storage expansion enclosure.
Fibre Channel loop and ID settings
When you install an E-DDM in the storage expansion enclosure, the E-DDM tray
plugs into a printed circuit board called the midplane. The midplane sets the Fibre
Channel loop ID automatically, based on the enclosure ID switch setting and the
physical location (bay) of the E-DDM.
Storage expansion enclosure ID settings
EXP520 and EXP810 storage expansion enclosures do not have enclosure ID
switches because the controllers automatically set the enclosure ID numbers.
Each storage expansion enclosure in a DS5020 storage subsystem drive loop must
have a unique enclosure ID. DS5020 controllers use a combination of the enclosure
ID and the number of the physical slot that a 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 storage expansion enclosures, you must use the
tens digit (x10) enclosure ID setting to distinguish different redundant drive channel
pairs and use the ones digit (x1) enclosure ID setting to distinguish storage
expansion enclosures IDs within a redundant drive channel.
The DS5020 normally ships with an enclosure ID outside the range of 00–77.
However, if your DS5020 enclosure ID was set to a value within the range of
00–77, it might be in conflict with the enclosure ID of one of the drive expansion
enclosures that you are trying to attach to the DS5020. If this is the case, the
amber ID Conflict LED on the storage expansion enclosure will light after you turn
on the power to the storage subsystem.
Give each storage expansion enclosure in a redundant drive channel pair 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 DS5020
controller will use soft AL_PAs for the devices that have identical hard AL_PAs.
The problem with soft AL_PAs addressing is that addresses might change between
LIPs. This possibility increases the difficulty of troubleshooting drive channel
problems, since one cannot easily ascertain whether the same device with a
different address or different device might be causing a problem. Set the enclosure
IDs in a given drive channel/loop pair to enforce hard AL_PAs addressing.
Connecting secondary interface cables
This section is applicable to (direct) out-of-band management configurations only. If
your configuration uses host-agent (in-band) management, skip this section.
Use the Ethernet interface ports on the back of the storage subsystem to connect
the controllers for direct management of the storage subsystems (see “Direct
(out-of-band) management method” on page 81).
78 IBM System Storage DS5020 Storage Subsystem: Installation, User’s, and Maintenance Guide