Re: Booting off of a MD striped drive?

Matthias Urlichs (smurf@smurf.noris.de)
Sun, 15 Sep 1996 14:08:41 +0100


In linux.dev.kernel, article <Pine.LNX.3.95.960908213812.1121B-100000@felix.intern>,
kraxel@cs.tu-berlin.de (Gerd Knorr) writes:
> On Fri, 6 Sep 1996, Adam J Megacz wrote:
>
> > Right now I have a root partition on the first one, and the rest of the
> > first one is striped with the second one. Is there a way to make them
> > into one BIG drive and just boot off of that (i.e., ardcode 'mdadd
> > /dev/md0 /dev/hda1 /dev/hdb1' into the kernel).

No. Nor would you want to. Seriously, it does make a lot of sense to have a
small and mostly-read-only root partition.

> > Could an initial ram
> > disk be used? Could I have a small root partition to set up the MD
> > device and then unmount that partition and remount /dev/md0 as root?

Yes. initrd can do that, thus the boot partition isn't used after loading
the RAM disk from it via the BIOS.

Currently, initrd can't use the disk directly because the kernel checks
that there's a real RAM disk loadded before starting /linuxrc. I don't know
how dangerous it would be to just throw away that check. For situations
like yours, or eg. for NFS root disks which need a bit more to set up than
the Ethernet interface, it would be a good idea -- it's stupid, IMHO, to
load an entore RAM disk just for the small parts of libc/sh/ifconfig/
/route/mount you'd need to set for that.

> But I don't know if LILO can handle md'ed drives. If not, you would have
> to boot from a floppy. Not that nice.
>
No, it can't.
>
> PS: I would prefere to be able to access the root fs as is, without having
> to run any tool before mounting it. This makes life much easier while
> troubleshooting something.
>
Right.
>
> Linux hackers are funny people: They count the time in patchlevels.
>
Too true...

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