[linux-lvm] Root on LVM and vgscan
Heinz J. Mauelshagen
Mauelshagen at sistina.com
Mon May 28 16:14:12 UTC 2001
On Mon, May 28, 2001 at 01:44:34PM +0100, Dick Middleton wrote:
>
> Thanks for your answers - as usual they provoke more questions...
>
> > On Fri, May 25, 2001 at 09:28:34AM +0100, Dick Middleton wrote:
> > > I have root running on lvm on sw raid partitions on linux 2.2.18. It all
> > > works fine. However I have had difficulty during booting after adding new
> > > LVs. The symptom is that the initial mounts of LVs fails or the wrong
> > > partition is mounted.
> > >
> > > What happens is that vgscan is run during the initrd phase and so the lvmtab
> > > is updated on the ram disk. Once the root file system on the hard disk has
> > > been mounted the lvmtab on that comes into use. That has not been updated by
> > > vgscan and so does not reflect the changes.
> > >
> > > Obviously it's possible to run vgscan again (between remounting root rw and
> > > checking the other discs) to update the lvmtab but it does beg a few
> > > questions.
>
> > Yes, that's the option (forcing some overhead).
> > The other would be to get the actual /etc/lvmtab* from the initial ram disk :-)
>
> Ah yes, I discovered that it lives in /initrd! Can I assume from this that
> it's safe to copy the lvmtab. Is that a good solution?
Sure.
This has the actual vgscan results *and* causes as little overhead as possible
to get it into the real root.
>
> > >
> > > 1) why does mount use the data in lvmtab and not in /proc to find out about
> > > active VGs?
>
> > mount doesn't access /etc/lvmtab* at all.
>
> Now you've got me. Why/how does mount mount the wrong partition when lvmtab
> is out of date if it doesn't access lvmtab? Are /dev/<vg>/<lv> updated by
> vgscan as well? It looked to me as if they weren't. Do they need to be copied
> from /initrd too?
Actually I've been too brief before :-(
The device nodes in your real root are the ones created *before* vgscan
was called from linuxrc and are likely out of date WRT to the minor numbers
they contain.
Something like
/dev/VGName/LVname 58 1
could be in your real root *but*
/dev/VGName/LVname 58 2
could have been updated by the vgscan run in the initial ram disk fs.
IOW: you can copy the /etc/lvmtab* files from the initial ram disk *and*
run vgmknodes(8) from your real root based startup script *before* the
VG is accessed (eg. to mount a fs).
>
> What should I read to better understand how all this works?
>
> Dick
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> read the LVM HOW-TO at http://www.sistina.com/lvm/Pages/howto.html
--
Regards,
Heinz -- The LVM Guy --
*** Software bugs are stupid.
Nevertheless it needs not so stupid people to solve them ***
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Heinz Mauelshagen Sistina Software Inc.
Senior Consultant/Developer Am Sonnenhang 11
56242 Marienrachdorf
Germany
Mauelshagen at Sistina.com +49 2626 141200
FAX 924446
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