LVM

[Shawn Badger]

I started using it because that is what everyone around here calls problems.
I think it is one of the new cooperate buzz words.  I noticed that you
didn't have to do a vgimport to make it work. I was told that I needed to do
that before I could do the vgchange, guess not.

Thanks for your help.



On Wed, Apr 16, 2008 at 2:04 PM, Matt Graham <danceswithcrows at usa.net>
wrote:

> After a long battle with technology, Shawn Badger wrote:
> > I don't have this issue with anything critical,
>
> Why do people call problems "issues"?  (I've asked this in multiple places
> for
> years now, and never gotten a coherent answer.)
>
> > but I know the time is coming. I know how to [recover LVs] when I have
> the
> > original system, but I would like to find a reliable way when someone
> brings
> > me a drive from a dead system and wants to pull data off of it.
>
> The problem is very badly specified.  If the PV is damaged in some way
> (creeping bad sectors, head crash, whatever) then all bets are off.  If
> the
> PV was part of a multiple-PV VG, then it's a crapshoot as to whether you
> can
> recover individual LVs for obvious reasons.  If the PV was the only PV in
> a
> VG, then it becomes easier.
>
> So:  I created a PV on a test disk, made a VG called "testvg" on it, made
> an
> LV called "testlv" on that VG, mke2fs'ed, mounted, and copied a bunch of
> data
> over.  I then umounted the LV and did vgchange -a n testvg.  Then, I
> unplugged the disk and connected that disk to another machine that had
> never
> had any PVs connected to it.  I then ran pvscan followed by vgchange -a y,
> and lvm2 found the VG and LV.  I mounted the LV on this machine and ran
> md5sum on everything, finding no differences from the originals in
> anything.
>
> This little example shows me that moving PVs between systems can work.
>  It's a
> bit contrived though.  In the real world, you'd probably have to insert a
> vgrename in there before the vgchange -a y, since too many distros call
> their
> VGs "vg00" or something unimaginative like that.  Also, the disk I used
> had
> no data corruption and was deactivated before being unplugged.  The man
> pages
> indicate that if the PV (not the VG, not necessarily) is corrupt,
> re-running
> pvcreate on the partition may salvage it.  If the LV structures get
> corrupted, I don't know what the heck you'd do.  Anyway, HTH,
>
> --
>   That which does not kill us makes us stranger.
>   --Trevor Goodchild, Aeon Flux
>   My blog and resume: http://crow202.dyndns.org:8080/wordpress/
> Matt G|There is no Darkness in Eternity/But only Light too dim for us to
> see
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