IBM DS6000 Series manual RedHat Enterprise Linux RH-EL multiple LUN support, 317

RedHat Enterprise Linux (RH-EL) multiple LUN support

RH-EL by default is not configured for multiple LUN support. It will only discover SCSI disks addressed as LUN 0. The DS6000 provides the volumes to the host with a fixed Fibre Channel address and varying LUN. Therefore RH-EL 3 will see only one DS6000 volume (LUN 0), even if more are assigned to it.

Multiple LUN support can be added with an option to the SCSI midlayer Kernel module

scsi_mod. To have multiple LUN support added permanently at boot time of the system, add the following line to the file /etc/modules.conf:

options scsi_mod max_scsi_luns=128

After saving the file, rebuild the module dependencies by running:

depmod -a

Now you have to rebuild the InitialRAMDisk, using the command:

mkinitrd <initrd-image> <kernel-version>

Issue mkinitrd -hfor more help information. A reboot is required to make the changes effective.

Fibre Channel disks discovered before internal SCSI disks

In some cases, when the Fibre Channel HBAs are added to a RedHat Enterprise Linux system, they will be automatically configured in a way that they are activated at boot time, before the built-in parallel SCSI controller that drives the system disks. This will lead to shifted special device file names of the system disk and can result in the system being unable to boot properly.

To prevent the FC HBA driver from being loaded before the driver for the internal SCSI HBA you have to change the /etc/modules.conf file:

￿Locate the lines containing scsi_hostadapterx entries where x is a number.

￿Reorder these lines: first come the lines containing the name of the internal HBA driver module, then the ones with the FC HBA module entry.

￿Renumber the lines: no number for the first entry, 1 for the second, 2 for the 3rd, and so on.

After saving the file, rebuild the module dependencies by running:

depmod -a

Now you have to rebuild the InitialRAMDisk, using the command:

mkinitrd <initrd-image> <kernel-version>

Issue mkinitrd -hfor more help information. If you reboot now, the SCSI and FC HBA drivers will be loaded in the correct order.

Example A-12shows how the /etc/modules.conf file should look with two Adaptec SCSI controllers and two QLogic 2340 FC HBAs installed. It also contains the line that enables multiple LUN support. Note that the module names will be different with different SCSI and Fibre Channel adapters.

Example: A-12 Sample /etc/modules.conf

scsi_hostadapter aic7xxx scsi_hostadapter1 aic7xxx scsi_hostadapter2 qla2300

Appendix A. Operating systems specifics 317