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1 containing even numbered LUNs (the bus bit is the LUN byte is always 0) while Bus 2 will only have odd numbered LUNs (the bus bit is the LUN byte is always 1).
Some Fibre Channel host adapters are set to only address LUNs 0 through 7 by default. This corresponds to only the first three bits in byte 1 of the FCP_LUN field. The bus designator is taking up one of these bits, leaving only two of the Target bits to address devices. This means that with the default settings of the FibreBridge, you are limited to four devices per FibreBridge SCSI channel, and they must be set to IDs 0 through 3. Depending on how many SCSI devices are connected to the bridge, and the IDs that they are set to, the host adapters may need to be configured to support more LUNs. Refer to the manual supplied with the host adapter for instructions on making this change.
As an example, consider the following configuration:
∙Say a FibreBridge has its Hard ID set to 3 and is using the default LUN value of 14
àFibreBridge will be detected at ID 3 LUN 14
∙You set the ID of a SCSI drive #1 connected to Bus 1 of the FibreBridge to 1
LLL = 000 TTTT = 0001 B = 0
LUN Byte: LLLT TTTB à 0000 0010 = Fibre Channel LUN 2
àSCSI drive #1 will be detected at ID 3 LUN 2
∙You set the ID of SCSI drive #2 connected to Bus 2 of the FibreBridge to 1
LLL = 000 TTTT = 0001 B = 1
LUN Byte: LLLT TTTB à 0000 0011 = Fibre Channel LUN 3
àSCSI drive #1 will be detected at ID 3 LUN 3
∙You set the ID of a SCSI RAID Controller on Bus 1 of the Bridge to 0
LLL = 000 TTTT = 0000 B = 0
LUN Byte: LLLT TTTB à 0000 0000 = Fibre Channel LUN 0
àRAID Controller will be detected at ID 3 LUN 0
∙You set the ID of a RAID group connected to the controller to 2
LLL = 010 TTTT = 0000 B = 0
LUN Byte: LLLT TTTB à 0100 0000 = Fibre Channel LUN 64
àRAID group will be detected at ID 3 LUN 64
For this configuration, all of the devices would be detected except for the RAID Group. This is because the translated LUN would be 64. Most operating systems, and Fibre Channel host adapters are not capable of supporting LUNs over 31. One way to compensate would be to change the address translation of the FibreBridge as follows:
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