[linux-lvm] LVM2 snapshots on root fs

[linux-lvm] LVM2 snapshots on root fs

[Thomas Klaube]

Hi,

we are using lvm (lvm version 1) snapshots for backup purposes for some
time without any problems. 

Whenever I try to create a LVM (version 2) snapshot of the lvm
containing the root fs my machine crashes. I am using SuSE 9.1 (kernel
2.6.5, lvm2-2.00.15, device-mapper-1.00.09), but I also tried a unpatched 
2.6.8.1 kernel with the redhat lvm2-2.00.21 and device-mapper-1.00.19
rpms. Same result... I can't create snapshots of the lvm with the root
fs, other lvm snapshots are ok.

Is this a known lvm2 problem? If it is a kernel issue, are there any
patches?

Regards
Thomas Klaube

Re: [linux-lvm] LVM2 snapshots on root fs

[Alasdair G Kergon]

On Tue, Sep 07, 2004 at 01:03:30PM +0200, Thomas Klaube wrote:
> Whenever I try to create a LVM (version 2) snapshot of the lvm
> containing the root fs my machine crashes. I am using SuSE 9.1 (kernel

We don't support pvmove or snapshots of volumes used by the tools themselves.

It is possible to snapshot the root volume, but the method is probably 
distribution-specific. Certain changes to the tools may make it easier
to support: a general parameterised script might be possible.

Alasdair
-- 
agk@redhat.com

Re: [linux-lvm] LVM2 snapshots on root fs

[Brian J. Murrell]

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On Tue, 2004-09-07 at 19:17 +0100, Alasdair G Kergon wrote:
> 
> We don't support pvmove or snapshots of volumes used by the tools themselves.

That seems rather limiting.  Is this something that should change in the
future?

> It is possible to snapshot the root volume, but the method is probably 
> distribution-specific.

Like what?  Using a copy of the /sbin/lvm2 binary not living in the
rootfs when you want to snapshot it?  What about /lib/libdevmapper.so.*?
Does it have the same problem?

b.


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Re: [linux-lvm] LVM2 snapshots on root fs

[Thomas Klaube]

On Tue, Sep 07, 2004 at 02:26:03PM -0400, Brian J. Murrell wrote:
> On Tue, 2004-09-07 at 19:17 +0100, Alasdair G Kergon wrote:
> 
> > It is possible to snapshot the root volume, but the method is probably 
> > distribution-specific.
> 
> Like what?  Using a copy of the /sbin/lvm2 binary not living in the
> rootfs when you want to snapshot it?  What about /lib/libdevmapper.so.*?
> Does it have the same problem?


Just copying /sbin/lvm2 to some other (non root) lvm does not do the 
job for me. Even if it worked it seems to be an ugly workaround. 

The question is, if there are plans to change the snapshot capabilities
of lvm2 in a way, that makes it possible to create snapshots even if the
tools reside on the lvm.

Regards
Thomas Klaube