Re: [Xen-users] RE: Tutorial : Debian, Xen and CLUSTER / GFS Supp ort

[Molle Bestefich <molle.bestefich@xxxxxxxxx>]

PAINCHAUD Christophe wrote:
> For my LVM/DM snapshot tests, I have created 4 block devices of 8GB in LVM
> group of 50GB. I am using DM and LVM2 libs and daemon from the Debian Etch
> packages. I wrote a program to write randomly in the 4 block devices (it
> looks like it's write about 20MB/s, I didn't really optimize it.). While
> this program is active, I do a snapshot of the first volume, and copy it on
> a tape device, I destroy snapshot, then do the same with second, third and
> fourth volume. I launched the loop of snapshot/backups many times in day
> without a single problem.

I'm very impressed!

> > I've got an HP ProLiant (x86_64)

> My test were made on a Dell 1750 (32bit) with a Perc 3D/I SCSI card.
>
> Did you experience any problem?

Yes.  I took one snapshot of a 3GB full 20GB ext3 volume onto a 10GB
snapshot target volume.  After executing the LVM2 snapshot command,
the original 20GB volume was trashed.  Seems like all disk accesses to
the 20GB volume were misaligned by a few kB's or so.  I could see
directories and files, but only because that's cached in RAM. 
Contents of all files were swapped randomly.  Totally trashed.

I wrote a bug report to dm-devel and got no replies.
I wrote a bug report to RedHat (Fedora Core 4, which I was using at
the time) and got no replies.

:-/.

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