[linux-lvm] Root on LVM and vgscan

[Heinz J. Mauelshagen]

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 :-)

> 
> 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.

The problem is that minor numbers are not striktly related to logical volumes;
they are associated at vgscan time.

> 
> 2) if lvmtab is so essetial why is it not updated by vgcreate/lvcreate and
>    other utilities when changes are made?

See above.

> 
> 3) would it not be possible/better to update lvmtab from /proc without doing
>    a rescan.

That could only be partially done, because /etc/lvmtab* contains the complete
metadata whereas /proc doesn't.

> 
> I don't know the issues involved and reasoning behind the design of this
> aspect of LVM but it does seem to me that there is something less than ideal
> in the current scheme.

The virtuall assignement of minor numbers to LVs causes the problem in the
root on LVM (and NFS) case. That'l likly be changed anyway.

> 
> Dick
> _______________________________________________
> linux-lvm mailing list
> linux-lvm at sistina.com
> http://lists.sistina.com/mailman/listinfo/linux-lvm
> 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 ***

=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-

Heinz Mauelshagen                                 Sistina Software Inc.
Senior Consultant/Developer                       Am Sonnenhang 11
                                                  56242 Marienrachdorf
                                                  Germany
Mauelshagen at Sistina.com                           +49 2626 141200
                                                       FAX 924446
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-