[Gluster-users] Performance in VM guests when hosting VM images on Gluster

Torbjørn Thorsen torbjorn at trollweb.no
Thu Mar 7 08:32:30 UTC 2013

On Tue, Mar 5, 2013 at 1:57 PM, Torbjørn Thorsen <torbjorn at trollweb.no> wrote:
> On Fri, Mar 1, 2013 at 7:01 PM, Brian Foster <bfoster at redhat.com> wrote:
>> On 03/01/2013 11:48 AM, Torbjørn Thorsen wrote:
> A degraded loop device without an open fd will be fast after a toggle
> of write-behind.
> However, it seems that an open fd will keep the loop device slow.
> I've only tested that with Xen, as that was the only thing I had with
> a long-lived open fd to a loop device.
>> Also, what gluster and kernel versions are you on?
> # uname -a
> Linux xen-storage01 2.6.32-5-xen-amd64 #1 SMP Sun May 6 08:57:29 UTC
> 2012 x86_64 GNU/Linux
> # dpkg -l | grep $(uname -r)
> ii  linux-image-2.6.32-5-xen-amd64      2.6.32-46
> Linux 2.6.32 for 64-bit PCs, Xen dom0 support
> # dpkg -l | grep gluster
> ii  glusterfs-client                    3.3.1-1
> clustered file-system (client package)
> ii  glusterfs-common                    3.3.1-1
> GlusterFS common libraries and translator modules

I've now tested with a newer kernel, and I'm seeing pretty much the
same thing there.

# dpkg -l | grep $(uname -r)
ii  linux-image-3.2.0-0.bpo.4-amd64     3.2.35-2~bpo60+1
Linux 3.2 for 64-bit PCs

After a while the loop device and Xen instance is slow, and profile
tells me it's only seeing 4kb writes.
Toggling the write-behind translator off and on again gets me back to
the initial transfer rate.

Contrary to what I have said earlier, this time I saw the transfer
rate change on a running Xen instance.
As far as I can tell, this means the transfer rate change also affects
open fd-s to the loop device.

I'll try filing a bug in the tracker that was mentioned in the

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Torbjørn Thorsen
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