Re: GRUB2, GPT, mdadm & LVM

[Andrey Borzenkov]

В Thu, 18 Jul 2013 20:35:43 +0200
Sander Smeenk <address@hidden> пишет:

> Quoting Chris Murphy (address@hidden):
> 
> > > During boot, GRUB starts and drops to 'grub rescue>' stating "Error:
> > > disk lvm/fdi-host_root not found".
> > 
> > This means it's not finding normal.mod or grub.cfg.
> 
> Yep. ;)
> 
> 
> > [..] So it's a bit curious that it's looking for its files on an lvm
> > root rather than on /boot. 
> 
> I could have stated that clearer indeed.
> /boot and everyting else is on the /dev/mapper/fdi-host_root LV.
> 
> I checked with 'set', the prefix= and root= settings seem correct:
> 
> root='lvm/fdi-host_root'
> prefix=(lvm/fdi-host_root)/boot/grub
> 
> But please note that doing 'ls' in the rescue shell does NOT show a
> 'device' named lvm/fdi-host_root or anything that would indicate it might
> be the LVM LV i need. Only (md/0) and all the (hdX/gptY) 'devices' show.
> 
> 
> > > Typing 'ls' in the rescue shell shows
> > > the '(md/0)' device, but LVM is never started by GRUB.
> > Only if /boot/grub files are also on LVM is that needed, in which case
> > lvm.mod needs to have been baked into the core.img. But the fact that
> > you're getting this message sounds like it's not loading lvm.mod.
> 
> So it seems. Yet, if i type 'insmod lvm' in the grub rescue shell, there
> is no error returned. This would indicate to me that the .mod was
> (already?) loaded correctly, because if i type 'insmod foobar' instead,
> grub complains it can't read/find the host_root LV, which is correct
> since 'foobar' isn't in core.img so grub would have to load it from
> disk..
> 
> 
> > I forget, but lsmod might work in the grub rescue shell to list what
> > modules are available in core.img.
> 
> It seems my core.img doesn't support lsmod. :(
> 
> 
> > > I tried (re)creating the core.img like so:
> > > | # grub-mkimage -o /boot/grub/core_lvm.img -O i386-pc \
> > > |     part_gpt part_msdos mdraid09 mdraid1x raid6rec \
> > > |     diskfilter lvm ext2
> > > And put that in all the disks:
> > > | # grub-bios-setup -b i386-pc/boot.img -c core_lvm.img /dev/sdX
> > You might be better off using grub-install --debug and figuring out
> > how it identifies the various parts.
> 
> Meh. Why didn't i think of doing that ;)
> " 'No errors reported.', okay then, that's not my problem! " :P
> 
> But all seems fine from the start:

Please paste exact command invocation and full output.

> | + abstractions=diskfilter mdraid1x raid6rec lvm
> | + grub_device=/dev/mapper/fdi-host_root
> | + devabstraction_module=diskfilter mdraid1x raid6rec lvm 
> | + prefix_drive=(lvm/fdi-host_root)
> 
> There is a small bug in the process where part_gpt gets added to the
> 'modules=' list for each disk in my system, resulting in:
> | + /usr/bin/grub-mkimage -d /usr/lib/grub/i386-pc -O i386-pc \
> |   --output=/boot/grub/i386-pc/core.img 
> --prefix=(lvm/fdi-host_root)/boot/grub \
> |  biosdisk ext2 part_gpt part_gpt part_gpt part_gpt part_gpt part_gpt \
> |  part_gpt part_gpt part_gpt part_gpt part_gpt part_gpt part_gpt \
> |  part_gpt part_gpt part_gpt diskfilter mdraid1x raid6rec lvm
> being called. However i would assume this is harmless...
> 
> Then grub-bios-setup runs. It scans all disks and logs:
> | info: Inserting hostdisk//dev/sdX into md/0 (mdraid1)
> for each of my disks. It's not actually raid1, but raid6,
> i'm not sure wether 'mdraid1' is an all purpose mdraid module?
> This *might* be an issue?
> 
> grub-setup continues nonetheless:
> | info: Scanning for lvm devices on disk md/0.
> | info: Found array fdi.
> | info: Inserting md/0 into fdi (lvm)
> |  [..]
> | info: guessed root_dev `lvm/fdi-host_root' from dir `/boot/grub/i386-pc'.
> | info: setting the root device to `lvm/fdi-host_root'.
> | info: the first sector is <2048,0,512>.
> perfectly true. It saves the sectors from 2048 to 2183, which seems the
> size of core.img and logs 'Installation finished. No error reported.'
> 
> 
> I'm at a loss :)
> 
> Thanks for your time,
> -Sndr.