[dm-devel] Issue in Root partition from SAN as device-mapper-multipath device

[Arumugam, Anburaja (STSD)]

> Hi,
> 
We are trying to get the root partition in a multipath device from a
SAN, in RHEL 4 U4 Beta. For this we have done the following things:

1. We set up a boot from SAN environment, with 3 partitions(/boot, /,
swap respectively) from a LUN on the SAN.
2. Without DM multipath, in GRUB.conf we had the parameter as
root=/dev/sda2, and it worked fine as expected
3. We want to set the / partition as a DM multipath device, and we
repackaged the initrd with the following as we felt these are required
by DM multipath to work at boot time:
3.1 modules in lib: dm-multipath.ko, multipath.ko, dm-round-robin.ko,
dm-zero.ko, dm-mod.ko
3.2 binaries in sbin (all static binaries): dmsetup, multipath, kpartx
3.2 config files in etc: multipath.conf, scsi_id.config,
40-multipath.rules
4. Our modified  init script in initrd looks as ;
.........
echo "Loading jbd.ko module"
insmod /lib/jbd.ko
echo "Loading ext3.ko module"
insmod /lib/ext3.ko
/sbin/udevstart
echo "Loading DM Module"
insmod /lib/dm-mod.ko
echo "Loading DM Multipath Module"
insmod /lib/dm-multipath.ko
echo "Execution multipath binary with v0"
/sbin/multipath -v 0
echo "Execution dmsetup"
/sbin/dmsetup ls --target multipath --exec "/sbin/kpartx -a"
echo Creating root device
mkrootdev /dev/root
umount /sys
echo Mounting root filesystem
mount -o defaults --ro -t ext3 /dev/root /sysroot
mount -t tmpfs --bind /dev /sysroot/dev
echo Switching to new root
switchroot /sysroot
umount /initrd/dev
5. Having the UUID returned by scsi_id for the root Lun is,
3600508b400102be10000100023750000, in GRUB.conf, we changed the
parameter as root=/dev/mapper/3600508b400102be10000100023750000p2 
6. rebooted the host, and it gave the following error.
"No devices found"
"mount: error  mounting ext3"

The reason behind this is as you know, No DM multipath device has been
created under /dev/mapper/ for root partition from the Lun, its unable
to mount the root '/' file system.

Can anyone help us by letting us know that, what are we missing in our
approach to create the DM multipath mapped devices for the root
partition diuring boot?

Thanks for your valuable inputs.

Regards,
Anbu
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