[linux-lvm] Root on LVM and vgscan

[Dick Middleton]

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?

>  > 
>  > 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is out of date if it doesn't access lvmtab?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?

What should I read to better understand how all this works?

Dick