[linux-lvm] vgimport/vgexport commands when logically moving disks between systems

[Dave]

Hi Patrick,

Thanks for clarifying the status of LVM1 (ie. *not* a clustering tool).  That's
somewhat surprising since it does include an LVM script in the resource.d directory.
 In any case, we're not in a huge rush to upgrade to LVM2 unless it really is
necessary, as these are RH AS3 boxes running the 2.4.21-47.ELsmp kernel, and the
docs I've read suggest LVM2 really needs/wants to run under a 2.6.x kernel.

If direct-io to metadata could be set as an option under LVM1, assuming that isn't
the default, that would be helpful.  But, it sounds like no one really wants to
support LVM1 anymore?!

Assuming we want to go forward with an upgrade to LVM2 on the current systems, how
involved is that procedure?  Do we risk losing all our data?

Thanks,
Dave

--- Patrick Caulfield <pcaulfie at redhat.com> wrote:

> Dave wrote:
> > Hi Patrick, et al.
> > 
> > Thanks for your comments!
> > I've been doing some testing on this topic, and encountering a bit of strange
> > behavior which seems to confirm the murkiness with switching VGs between hosts. 
> > Please bear with my lengthy description, as I'm trying to be as clear as
> possible. 
> > I really need to work this out.
> > 
> > THE TEST:
> > 
> > Hosts are P10 (primary node) and P11 (backup node)
> > VG is activated on P10 and fs is mounted.  To test a switch to P11, I deactivate
> the
> > VG on P10, but DO NOT run vgexport (following your suggestion).  I then, run
> > vgimport on P11 (but P11 reports it already knows about the VG - that's fine),
> and
> > then run an activate.  However, when I try to run an e2fsck on the fs, I get the
> > following error:
> > 
> > /sbin/e2fsck: No such device or address while trying to open /dev/tux-ao/app
> > Possibly non-existent or swap device?
> > 
> > However, the device does exist, and looks identical to the one on P10:
> > [P11]$ ls -l /dev/tux-ao/app
> > brw-rw----    1 root     disk      58,  14 Dec  6 14:46 /dev/tux-ao/app
> > 
> > I was able to fix the problem by putting vgexport back into the mix.  In this
> case,
> > I export the VG from P10 and then after an import on P11 I was able to run
> e2fsck
> > and mount successfully.  
> > 
> > Also, this (unknown VG) message is somewhat common in pvscan, if a vgexport is
> not
> > performed:
> > 
> >> pvscan -- inactive PV "/dev/sdk"  is associated to unknown VG "tux-ao" (run
> > vgscan)
> > 
> > 
> > Here is another clear example of some unexpected behavior (at least to me)...
> > 1. status when $vg on P11 successful - notice the status of ACTIVE on P11 and
> > EXPORTED on P10
> > 
> > [P11]$ sudo pvscan
> > pvscan -- reading all physical volumes (this may take a while...)
> >  ...
> > pvscan -- ACTIVE   PV "/dev/sdk" of VG "tux-ao"   [27.09 GB / 9.09 GB free]
> > 
> > [P10]$ sudo pvscan
> > pvscan -- reading all physical volumes (this may take a while...)
> >  ...
> > pvscan -- inactive PV "/dev/sdk"  is in EXPORTED VG "tux-ao" [27.09 GB / 9.09 GB
> > free]
> > 
> > Then...
> > 2. status after $vg is deactivated on P11 and activated on P10 (no vgexport run
> on
> > P11 before activation on P10) - Notice the "unknown VG" message on P10!!!  
> > 
> > [P11]$ sudo pvscan
> > pvscan -- reading all physical volumes (this may take a while...)
> >  ...
> > pvscan -- inactive PV "/dev/sdk" of VG "tux-ao"   [27.09 GB / 9.09 GB free]
> > 
> > [P10]$ sudo pvscan
> > pvscan -- reading all physical volumes (this may take a while...)
> >  ...
> > pvscan -- inactive PV "/dev/sdk"  is associated to unknown VG "tux-ao" (run
> vgscan)
> > 
> > Then...
> > 3.  Then, when I tried an activation on P10 I get no joy at all (ie. cannot
> perform
> > operations on the logical volume), despite the fact that it exists:
> > [P10]$ ls -l /dev/tux-ao/app
> > brw-rw----    1 root     disk      58,  14 Dec  6 15:04 /dev/tux-ao/app
> > 
> > /sbin/e2fsck: No such device or address while trying to open /dev/tux-ao/app
> > Possibly non-existent or swap device?
> > 
> > Is this simply flakey behavior with LVM 1.0.8 ?
> > 
> > We have several VGs on the machine, and sometimes we need to move one or two at
> a
> > time.  LVM (v1) seems to have trouble here, at least without vgexport.  Anyone
> know
> > what might be happening behind the scenes to cause this behavior?  It's looking
> to
> > me like I really do need vgexport to make things work the way we want.
> > 
> > Thanks again for helping me to clarify this situation.
> 
> It's rather worrying that the two nodes seem to be reading different data from the
> same disks.
> I can't remember off-hand whether lvm1 does direct-io when it updates metadata,
> possibly not.
> In which case you might have to upgrade to lvm2 (which does).
> 
> lvm1 is /not/ a clustering tool ;-)
> 
> -- 
> 
> patrick
> 
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> read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/
> 



 
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