User`s guide

294 Implementing an Open IBM SAN
4.4 SCSI devices
The four SCSI ports on the SAN Data Gateway support Differential Ultra Wide
SCSI devices. It will automatically negotiate speed for wide or narrow bus width
devices as well as standard, fast and, ultra speeds. The SAN Data Gateway
provides a termination on each of its SCSI buses. The termination can be
separately disabled if so desired from the StorWatch SAN Data Gateway
Specialist window.
4.4.1 LUN support
The SAN Data Gateway provides support for up to 256 LUNs. Each SCSI
channel supports up to 15 SCSI targets and up to 32 LUN per target. This is
subject to the overall total of 256 available. The first LUN (LUN 0) is used for the
Gateway for control and command purposes. That leaves 255 allowable LUN
addresses to be used for attaching SCSI devices to the four SCSI ports.
The SCSI devices must be previously set up in your host prior to attaching to the
SAN Data Gateway. For example, if an IBM Enterprise Storage Server is to be
used as the target device, then all the volume or LUN assignments must be
completed. Also, the volumes should be assigned to the appropriate SCSI port in
the ESS. Attach the SCSI cable from the SCSI device to a SCSI port on the
Gateway.
4.4.2 Device discovery
Once attached, the SAN Data Gateway can be restarted or powered on to
perform a discovery of the attached devices. If this was done after the
initalizeBox command from the service terminal, then the initial discovery will
be carried out in a specific order. The buses are scanned in order from 1 to 4 and
each bus is scanned from SCSI target 0 to 15 and LUN 0 to 32 for each ID. As a
device is discovered it is assigned a specific LUN number by the SAN Data
Gateway. This numbering will begin at LUN number 1, zero is reserved for the
SAN Data Gateway control, and continues sequentially as devices are
discovered.
Note: Do not attach more than 255 LUNs to the SAN Data Gateway.
Exceeding the 255 limit will cause unpredictable results.