To enable multipathing on RedHat Linux 5.3 By Robert Tsai on Aug 10, 2009 Set multiple cable connections per your design such as dual connections from the server to the SAN switch and then to the storage array. At Sun Solution center, we use QLogic HBA and its driver can be downloaded directly from Qlogic web site. Check the HBA used and ensure to get the correct driver. i.e. the HBA model we used is QLE2462, download its driver accordingly from below: http://driverdownloads.qlogic.com/QLogicDriverDownloads_UI/default.aspx In Red Hat Enterprise Linux 5, device-mapper-multipath is installed by default. This is a change from Red Hat Enterprise Linux 4. If a third party multipathing solution is in use, device-mapper-multipath should be disabled to avoid any conflict between the multiple multipathing technologies. But RedHat multipathing is NOT ACTIVATED by default and you must enable it. To enable it, modify the setting in /etc/sysconfig/mkinitrd/multipath file by changing MULTIPATH from NO to YES MULTIPATH=YES By default, /etc/multipath.conf has all devices blacklisted. If this default configuration has been changed, the change should be reverted. Comment out following three lines: # Blacklist all devices by default. Remove this to enable multipathing # on the default devices. blacklist { devnode "*" } Then reboot. Enable the multipathd on boot and start it by chkconfig mutipathd on service multipathd start At this time, you should be able to see multiple connections to the LUNs on the storage array if everything set correctly and you can verify it using "fdisk -l". You should see some newly enabled "dm-??" devices. Also run "/sbin/multipath -ll" command and should see the path to each device. i.e. the path mpath2 for device dm-7 pointing to two devices sdj and sdx. mpath2 (3600a0b80004879f0000004064a5b5d9f) dm-7 SUN,CSM200_R [size=50G][features=1 queue_if_no_path][hwhandler=1 rdac][rw] _ round-robin 0 [prio=200][active] _ 0:0:1:2 sdj 8:144 [active][ready] _ 1:0:1:2 sdx 65:112 [active][ready] _ round-robin 0 [prio=0][enabled] _ 0:0:0:2 sdc 8:32 [active][ghost] _ 1:0:0:2 sdq 65:0 [active][ghost] You should see I/O activities on both sdj and sdx when running dd test on dm-7.[@more@]