The builder of this server installed device-mapper-multipath. It is thrashing our IBM DS4000 horribly. I want to turn this off and install the RDAC drivers provided by IBM. But the /etc/multipath.conf is virtually all commented out EXCEPT for "blacklist { devnode "*"}". Meanwhile multipath device list shows the following:
]# multipath -d -l
mpath1 (3600a0b800018cf3c000028aa475ffd51)
[size=200 GB][features="0"][hwhandler="0"]
\_ round-robin 0 [active]
\_ 1:0:0:41 sdc 8:32 [active]
\_ round-robin 0 [enabled]
\_ 1:0:1:41 sde 8:64 [active]
\_ round-robin 0 [enabled]
\_ 1:0:2:41 sdg 8:96 [active]
\_ round-robin 0 [enabled]
\_ 1:0:3:41 sdi 8:128 [active]
\_ round-robin 0 [enabled]
\_ 2:0:0:41 sdk 8:160 [active]
\_ round-robin 0 [enabled]
\_ 2:0:1:41 sdm 8:192 [active]

mpath0 (3600a0b800018cf3c00002841475e9cc7)
[size=60 GB][features="0"][hwhandler="0"]
\_ round-robin 0 [active]
\_ 1:0:0:40 sdb 8:16 [active]
\_ round-robin 0 [enabled]
\_ 1:0:1:40 sdd 8:48 [active]
\_ round-robin 0 [enabled]
\_ 1:0:2:40 sdf 8:80 [active]
\_ round-robin 0 [enabled]
\_ 1:0:3:40 sdh 8:112 [active]
\_ round-robin 0 [enabled]
\_ 2:0:0:40 sdj 8:144 [active]
\_ round-robin 0 [enabled]
\_ 2:0:1:40 sdl 8:176 [active]

Where is this configured? Besides doing a "chkconfig -multipathd off" and commenting out the two device specs in the /etc/fstab before the next reboot, what do need to do to turn this off?

Remove the device-mapper-multipath package and reboot. Otherwise the module will always be loaded. Or you could blacklist that. But if you're going to use RDAC, no need for dm-multipath at all. Easy enough to re-install later.