IBM DS3950, Installation, User'S, And Maintenance Manual, Page: 106 / 252

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
EXP395 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 DS3950 storage subsystem drive loop must
have a unique enclosure ID. DS3950 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 DS3950 normally ships with an enclosure ID outside the range of 00–77.
However, if your DS3950 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 DS3950. 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 DS3950
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).
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IBM System Storage DS3950 Storage Subsystem: Installation, User’s, and Maintenance Guide