Re: md extension to support booting from raid whole disks.

["H. Peter Anvin" <hpa@zytor.com>]

Neil Brown wrote:
> 
> Having a replicated boot loader and having a raid1 are conceptually
> quite different things.
> A raid1 says "keep N (typically 2) copies of the data somewhere for
> me".
> A replicated boot loader says "store this boot loader on every
> bootable device".
> One is more abstract, the other is more concrete.
> 
> Maybe it is a very subtle distinction, but I think it is worth
> maintaining.  Get your boot-loader-installer to install at the front
> of every drive - don't bother having a raid1 there that is never read
> and hardly ever written..
> 

I think it is an unfortunate distinction (although I see why you want to
make it), and one which goes in the wrong direction.

As I've stated many times (and not just in this debate), I believe using
the RAID-1 mechanism to replicate /boot across the entire span of
devices is the right thing to do.  Not just the boot loader, but all of
/boot.

Once you do that, you do want to write it on a regular basis, and using
the RAID-1 code is the obvious way to do it.  You can argue that it is
an accidental effect of the way the current Linux RAID-1 code does it,
but it's nevertheless extremely useful, widely deployed, and extremely
resilient.

	-hpa

-- 
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel.  I don't speak on their behalf.