How can I install my root filesystem on a multipathing device? (/dev/mapper/mpath0)

Hi Experts,

I'm installing RHEL 5.4 on a native LPAR of System Z (z10BC) mainframe, which is connected to DS8300 via FCP. Here are my details:

[root@zlnx1 ~]# uname -a
Linux zlnx1 2.6.18-164.el5 #1 SMP Tue Aug 18 15:53:50 EDT 2009 s390x
s390x s390x GNU/Linux

[root@zlnx1 ~]# lsscsi
[0:0:0:1]    disk    IBM      2107900          .116  /dev/sda
[0:0:0:2]    disk    IBM      2107900          .116  /dev/sdb
[1:0:0:1]    disk    IBM      2107900          .116  /dev/sdc

[root@zlnx1 ~]# lszfcp -D
0.0.2200/0x500507630803005e/0x4016400000000000 0:0:0:1
0.0.2200/0x500507630803005e/0x4016400100000000 0:0:0:2
0.0.2300/0x500507630803405e/0x4016400100000000 1:0:0:1

[root@zlnx1 ~]# df
Filesystem           1K-blocks      Used Available Use% Mounted on
/dev/sdb1              6092360   2658584   3119308  47% /
/dev/sda1               194442     15342    169061   9% /boot
tmpfs                  1029532         0   1029532   0% /dev/shm

Basically, /dev/sdb and /dev/sdc points to the same disk. And I would like to setup a multipathed device (e.g. /dev/mapper/mpath0) which points to /dev/sdb /dev/sdc and mount my root file system there.

Here are the steps I have done so far:
- My root is installed originally in /dev/sdb1
- My /boot is installed in /dev/sda1
- I have setup my second path /dev/sdc (same disk/LUN with /dev/sdb)
- I have correctly updated my /etc/multipath.conf
- Then recreate initrd, ===> mkinitrd -v --with=dm-mod --with=dm-multipath --with=dm-round-robin initrd-2.6.18-164.el5.img 2.6.18-164.el5
- Then zipl and reboot, ===> zipl -V

Am I missing something?
How can I start multipathing on Root before mounting my Root filesystem?

I hope you can give me some detailed example. Thank you very much.

Regards,
Dave