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Re: backing up LVM volumes



On Tue, 27 Apr 2010 16:40:37 -0500
"Boyd Stephen Smith Jr." <bss@iguanasuicide.net> wrote:

> On Tuesday 27 April 2010 16:03:55 Celejar wrote:
> > I've had to give up lvm snapshots totally as
> > broken, primarily because of this (see my messages in the thread):
> > 
> > http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=549691
> 
> That is troublesome, probably to the point of actually being broken.  It's 
> likely that something "behind-the-scenes" in LVM is actually messing with the 
> snapshot device even when it is not mounted and preventing the removal.

Makes sense to me, although I'm no expert.
 
> I'm fairly sure the snapshot device has to be updated whenever a write is done 
> to a new LE in the original device, and it's possible *that* is causing the 
> problem.  I hope this issue gets some attention; I doubt it is a Debian-ism.

The mechanism is somewhat documented in the source tree at
Documentation/device-mapper/snapshot.txt, although I'd have to read it
more carefully.

> > I've also been hit by this, although it *may* be harmless (or not -
> > this stuff could really use decent documentation):
> > 
> > http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=503268
> 
> My guess on this one is one of two things:
> 1) Udev is taking a little while to unlink "secondary" names for the LVs that 
> are being removed, and when lvm does its device scan it's hitting "missing" 
> devices.
> 2) LVM is using device names from its cache for devices that are no longer 
> present for its device scan and, again, hitting "missing" devices.
> 
> In either case I think the error messages are annoying, but not indicative of 
> a real problem.

Makes sense.  I don't think that I've ever experienced an actual
problem obviously related to this, although it may, of course, be
symptomatic of something actually wrong with my setup.

Celejar
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