Re: GRUB bug with Btrfs multiple devices

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On Sat, Nov 30, 2019 at 10:14 AM Chris Murphy <lists@xxxxxxxxxxxxxxxxx> wrote:
>
> On Sat, Nov 30, 2019 at 10:02 AM Andrei Borzenkov <arvidjaar@xxxxxxxxx> wrote:
> >
> > GRUB is normally using hints - grub-install (and grub-mkconfig) tries to
> > guess firmware device name. At boot time grub tries to access hinted
> > device first, if it succeeds, it does not try anything else. With second
> > btrfs partition grub needs to find second device at boot time so it now
> > probes everything and hits those vendor media devices.
> >
> > At least this explains what you see as well as ...
> >
> > > Last time this
> > > happened, all I did was remove the 2nd device and the problem went
> > > away.
> >
> > ... this.
>
> Ahhh, that makes complete sense. So it is Btrfs multiple device
> related, but not a bug in btrfs.c per se.
>
> >
> > If you go in grub shell in this state (without errors), do you see those
> > ghost devices?
>
> Uncertain. My vague memory recall is that yes they are there, because
> I found their existence strange and different compared to pre-GRUB
> 2.02 where on this same system I'd see only either hd0 or hd1 (one
> without the other), along with cd0. But something changed either with
> a firmware update from Apple, or GRUB, that resulted in additional
> GRUB devices, hd2, hd3, hd4, hd5.

OK my vague memory  is correct with respect to phantom devices still
present after Brfs device removal.


>
> > > I'm ready to try that again (remove the 2nd device) and see if
> > > the problem goes away, but has enough information been collected about
> > > the present state?
> > >
> > >
> >
> > If you are reasonably sure that all errors are related to those phantom
> > devices - I would say yes, the reason for these phantom devices to exist
> > is already clear.
>
> I'll give it a shot in a bit.

Yep, the errors no longer happen; but phantom devices still there.
I've posted to grub-devel@ and updated it with this latest
information.


-- 
Chris Murphy



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