How do I setup multiple LUNs on Red Hat Enterprise Linux?

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 Issue

• How do I setup multiple LUNs on Red Hat Enterprise Linux?
• receive message "kernel: scsi: On host 3 channel 0 id 1 only 511 (max_scsi_report_luns) of 522 luns reported, try increasing max_scsi_report_luns"
• need to see more than 511 luns
• how do I configure max_luns and max_report_luns for the scsi_mod kernel module?
• In releases prior to RHEL 6 the scsi_mod module parameters such as, max_luns and max_report_luns could be changed by modifying /etc/modprobe.conf, how do I do the same in RHEL 6?

Resolution

• There is a parmeter of SCSI core module to control the number of multiple LUNs.
• Listed below are the steps to configure multiple LUNs.

For Red Hat Enterprise Linux 3, 4, 5

1. Modify the kernel module configuration file.

In Red Hat Enterprise Linux 3, you need modify /etc/modules.conf, please add the following line.

options scsi_mod max_scsi_luns=xxx

In Red Hat Enterprise Linux 4 and Red Hat Enterprise Linux 5, /etc/modprobe.conf is used.

options scsi_mod max_luns=xxx

2. Build the initial ramdisk to implement the change
3. # mkinitrd -f /boot/newimage-2.6.xx 2.6.xx

(add the exact kernel version you have in place of xx)

4. Reboot the system. After the reboot, the LUNs should appear.

For Red Hat Enterprise Linux 6

1. scsi_mod is now built in to the kernel and is no longer a loadable module as in prior versions. Therefore module options cannot be changed in RHEL 6 by adding a .conf file entry within the /etc/modprode.d directory. Settings should go on the kernel command line. Append the following to your grub.conf 'kernel' line:
2. scsi_mod.max_luns=xxx
3. Note that some new arrays also require the report luns entry value be set. If so, also append it to your grub.conf kernel line:
4. scsi_mod.max_report_luns=xxx
5. Reboot the system. After the reboot, the LUNs should appear.

Diagnostic Steps

• The default setting for lpfc.lpfc_max_luns (Emulex HBAs) is 255. This can be checked with the following command.

# cat /sys/module/lpfc/parameters/lpfc_max_luns

255

• The default setting for qla2xxx.ql2xmaxlun is 65535. This can be checked with the following command (RHEL5 and above only).

# cat /sys/module/qla2xxx/parameters/ql2xmaxlun

65535

• The default setting for scsi_mod.max_luns (SCSI mid layer) is 512. This can be checked with the following command.

# cat /sys/module/scsi_mod/parameters/max_luns

512