HOW-TO enable multipathing on RedHat Linux 5.x

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.