I think this question is regarding adding LUNs on a SCSI bus  that have non-consecutive numbers.  SLES distros used to have this scsi_sparselun option so you could scan if there was a LUN 1 and 5 but no LUNs numbered 0, 2, 3, and 4 for example.  Also, RHEL 3/4 distros used to only support 1 SCSI device per target out-of-the-box.

As Daniel says, RHEL 5 distros don't require any modprobe.conf changes to support multiple scsi devices per target -- the default max_luns number seems to be 512 as of 5.1.  Some RHEL 4 distros may require the "options scsi_mod max_luns=128" to be added to modprobe.conf and the ramdisk re-created.

Also, I have not tried this lately, but there is a default_dev_flags option to scsi_mod that is available to let you scan for "sparse" or non-consecutive LUN numbering schemes at boot time.  I'm not entirely sure what this value would be (since I don't have a way to try), but I suspect it would be something like default_dev_flags=0x240.  I'm also not clear on what the default is for all RHEL kernel versions.  If /sys is to be believed, the default is to not scan for SPARSE LUNs at boot time.

Now as to scanning for these LUNs on a running system, we use the ubiquitous rescan-scsi-bus.sh script with the "--nooptscan" option and I can hot-add non-consecutive LUNs to my system. 

Hopefully, this is useful.  If someone has tried any "default_dev_flags" configuration, I'd love to hear about it.








--
Dave Costakos
mailto:david.costakos@gmail.com

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