grub install/setup oddity

[Mark J Strawcutter]

Dell PE2850, RHEL4 AS installed from scratch.

/dev/sda and /dev/sdb identically partitioned

sda1 and sdb1 are md1 raid1 mounted /boot
sda2 and sdb2 are swap
sda3 and sdb3 are md3 raid1 mounter /

grub installed on sda as part of installation, systems booting fine.

In grub shell did:

device (hd0) /dev/sdb
root (hd0,0)
setup (hd0)

all worked fine without error.  But when I try to boot /dev/sdb I get thrown into
interactive grub (ie get grub prompt).  Even more interesting is that I can, at
this point, manually enter the root/kernel/initrd commands that are in the
grub.conf menu entry, followed by "boot" and the system comes up.

I then went into grub shell and did the device/root/setup commands on /dev/sda
and now it, too, throws me into interactive grub.

This says the install process "installed" grub differently than the device/root/setup
sequence is doing - the question is, different how?

BTW - I tried running "grub-install /dev/sdb" and get:

/dev/md1 does not have any corresponding BIOS drive.

Any suggestions what to try?  Thanks

Mark