Re: Linux not adhering to BIOS Drive boot order?

[Andreas Dilger]

Tim Fletcher writes:
> You can already do this, just specify /dev/md0 as the device to install
> onto, and lilo does the rest
> 
> > This would potentially allow you to boot from the second drive if the
> > first one fails, assuming the kernel does UUID or LABEL resolution for
> > the root device.  The kernel would boot from the first BIOS drive, and
> > would search for a UUID or LABEL as the root device.
> 
> I have a mirrored boot drive in a pair of firewalls / routers and to test
> before I put them into service I pulled hda and the machine booted fine
> from hdc and baring winging about the missing disk (all the drives are
> mirrored) carried on as normal. A fresh disk was put and rebuilt no
> problems and was then booted off with the other disk missing.

Ahh.  What I was missing was that by specifying /dev/md0 as the root device,
not only do you get an identical map for the kernels, but the root device
remains /dev/md0 no matter which drive fails and LILO/kernel don't need to
do anything special to find it.  This assumes the BIOS can boot from /dev/hdc
to start with (i.e. /dev/hda is totally gone).

How does MD/RAID0 know which array should be /dev/md0?  What if you had a
second array on /dev/hdb and /dev/hdd, would that become /dev/md0 (assuming
it had a kernel/boot sector)?

Cheers, Andreas
-- 
Andreas Dilger  \ "If a man ate a pound of pasta and a pound of antipasto,
                 \  would they cancel out, leaving him still hungry?"
http://www-mddsp.enel.ucalgary.ca/People/adilger/               -- Dogbert