Re: PATCH: allow installing grub on the MBR if /boot is on mdraid.

[Jeremy Katz <katzj redhat com>]

On Wed, 2008-12-03 at 09:36 +0100, Hans de Goede wrote:
> Jeremy Katz wrote:
> > On Tue, 2008-12-02 at 11:26 +0100, Hans de Goede wrote:
> >> Jeremy Katz wrote:
> >>> On Mon, 2008-12-01 at 18:58 +0100, Hans de Goede wrote:
> >>>> You are right studying the code further this does indeed happen. And installing 
> >>>> to the first sector of the raid set partitions should be fine, assuming that 
> >>>> the disk has a dos like mbr which just bootstraps to the bootsector of the 
> >>>> active partition, but what if the disk does not have a valid mbr?
> >>> This has come up from time to time.  One answer is that if we don't
> >>> detect something that looks like an MBR and we're doing this (or any
> >>> install /boot partition type installs), we should overwrite with a
> >>> "real" MBR.  The problem is that this could trample over some other boot
> >>> loaders which has been something we haven't been willing to do in the
> >>> past.  Maybe we should pop up a warning and default to doing so, but
> >>> give a way out if the user knows that they have a valid reason.  Even
> >>> though I hate those sorts of things :/
> >> I vote for just defaulting to installing on the MBR even in the raid1 case, if 
> >> the user wants the redundancy one gets from installing into the mdraid 
> >> partition, they can still easily select that. The user needs to have either a 
> >> special BIOS, or needs to modify the BIOS settings and / or remove the disk 
> >> when it died, which all require a very experienced user. I don't think it is to 
> >> much to ask this special group of users to change the selection from install to 
> >> mbr to install to partition during install if they want the additional 
> >> redundancy this gives.
> > 
> > That is a major change from what the behavior has been essentially
> > forever.  And it's the sort of change that leads to downtime and admin
> > cursing.  I really don't think that just installing to one MBR by
> > default if you're doing a RAID'd /boot is the intent or the desire... if
> > we're going to default to doing the MBR, then we need to do similar bits
> > to ensure that there's a boot record installed on both MBRs.
>
> Ok then how about still defaulting to the old behavior, but atleast allow 
> installing to the MBR in the raid1 case (which we currently do not allow)? Note 
> I don't have much of an opinion on this either way, I'm just trying to fix: 217176

I'm okay with allowing it.  I think it probably does make sense to also
do the check for if there's something MBR-looking on the MBR and ask if
not.  It won't be a great check, but I suspect at the granularity that
it gets seen, it'll be good enough

Jeremy