SCSI Devices with LUN > 0 on Linux
Posted by Sven Koester, Last modified by Sven Koester on 08 January 2010 10:01
Devices on the SCSI bus are addressed by their SCSI ID as major address and the logical unit as minor address. The are referred to as ID and LUN, where the very most devices have LUN = 0.
Some devices seem to have difficulties to handle a scan on the SCSI bus for LUNs > 0. Because of that, modern Linux kernels by default do not scan for LUNs > 0 on the SCSI bus.

As a result, SCSI devices with LUN > 0 are not visible to the system and are not recognized by PresSTORE. This can be checked
with the command:
   cat /proc/scsi/scsi
In case the device is not visible here, it has not been detected by the Linux kernel.

It is possible to add a device manually with the following command:
   echo "scsi add-single-device a b c d" > /proc/scsi/scsi
where:
    a == hostadapter id (first one being 0)
    b == SCSI channel on hostadapter (first one being 0)
    c == ID
    d == LUN (first one being 0)

In case the device becomes visible to PresSTORE after that change, you may want to enable the scan on the SCSI bus for LUNs > 0.
To achieve that, add the following line to the file /etc/modules.conf.local:
   options scsi_mod max_scsi_luns=128

After the next system start, devices with higher LUN should be detected automatically.
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