Don,
Yes, it certainly can be done. I do it all the time.
It's not hard with lilo, but grub doesn't support raid/md boot devices yet. This means that the grub boot record doesn't automatically get written to the second disk. In short, choose lilo for root mirroring if possible.
Ugh-blah. Excuse me folks, but.. maybe someone will be able to answer this one:
why the hell a boot loader should "mirror" anything to the second disk? :)
That is. Place standard MBR into the boot sector. An MBR that will boot from active partition. Be it e.g. /dev/hda and /dev/hdb. Create raid1 device from /dev/hda1 and /dev/hdb1. Mark both partitions as active. And install whatever boot loader you want into /dev/md1 - it will be mirrored automatically to /dev/hda1 and /dev/hdb1 (and to whatever else disks you'll use).
Should your first disk fail, the system will either not boot because of bios limitations, or bios may "remap" /dev/hdb into /dev/hda (to be 0x80), and in this case boot procedure will work.
Well, ok, a boot loader should be able to determine real offsets from the start of the disk, not from the start of raid device. I don't know whenever grub can do that - lilo apparently does, as all our systems are set up exactly this way...
/mjt
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