Re: Grub Failure when HDD descriptor changes

[Molle Bestefich]

Peter Jones wrote:
> Molle Bestefich wrote:
> > Dennis McMurchy wrote:
> > >   Thanks a million.  That got me on the right track, finally.
> > >
> > >   It didn't solve the problem right away, though, because it turned out
> > > that the 'device.map' file that was being generated was wrong in a way 
> > > that
> > > wasn't immediately obvious to me.  It was giving me this (even though
> > > the BIOS is set to boot from SCSI before IDE):
> > > [snip]
> > >   When I finally changed the 'device.map' manually to look like this (and
> > > updated 'grub.conf' accordingly, of course) everything worked just fine:
> > > [snip]
> > >   I don't know if this really qualifies as a bug or not, but I'm just
> > > delighted to have this working finally.
> >
> > This bit, together with HighPoint RAID corruption, has been keeping me
> > away from GRUB for years.
> >
> > As far as I understand, it's a wild guessing game that GRUB does,
> > which IMHO is just crazy.
> >
> > Then again, I don't know the guessing algorithm.
> > Can anybody elaborate?  Jason?
> 
> You *can't* solve this problem on x86.  There is no reliable way to ask
> the bios if it can address a disk, or what ID would have.
> 
> [explanation snipped]

Hi Peter

Thanks for the explanation.

As you've made clear, GRUB can't possibly know which Linux device maps
to which BIOS device.  I'd like to know why it attempts to do so
anyway, and what the (insane, I guess :-)) algorithm it uses is?

I think that in order to convince the general public to switch to
GRUB, it needs to more convincingly not destroy people's data.

Currently, it does this alot.

I've fixed a bug in GRUB and I'll maybe fix a couple more I spotted,
and perhaps add a single feature to protect the innocent.

But one of my biggest worries is that GRUB *per default* tries to do
some (again, probably insane?) guesses as to how the device map.

What's the algorithm and reasoning behind?