KVM / Qemu Images doesn't work with ceph-fs

KVM / Qemu Images doesn't work with ceph-fs

[Christoph Raible]

Hi @all,

in an other mail (http://marc.info/?t=130442346600006&r=1&w=2)
I explained my Config. And after two changes in the config file
the ceph-fs works fine :)

Now I want to use image-files (qcow2, raw or img filetype) with KVM.

This doesn't work.

When I do a fresh isntallation / creation with virt-install:


virt-install --connect qemu:///system -n vm18 -r 512 --vcpus=2 -f 
/ceph/vm18.qcow2 -s 10 -c /tmp/debian-6.0.1a-amd64-netinst.iso --vnc 
--vncport=5961 --vnclisten=0.0.0.0 --noautoconsole --os-type linux 
--os-variant generic26 --accelerate --network=bridge:br0 --hvm

The creation of the file works but on installation following errors occur:

http://www.christoph-raible.de/diskerror.png
http://www.christoph-raible.de/diskerror2.png


When I create a VM with virt-manager the creation of the disk hangs on 
the following step (creating Domain):

http://www.christoph-raible.de/diskerror3.png



I have no idea whats wrong a

   dd if=/dev/zero of=meineDatei bs=1024 count=10000

works perfect...


I doesn't have any ideas what's wrong.
Creation of a VM directly on the filesystem (without ceph) works fine.



Regards,

Christoph
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Re: KVM / Qemu Images doesn't work with ceph-fs

[Tommi Virtanen]

On Thu, May 05, 2011 at 11:45:27AM +0200, Christoph Raible wrote:
> in an other mail (http://marc.info/?t=130442346600006&r=1&w=2)
> I explained my Config. And after two changes in the config file
> the ceph-fs works fine :)

Are you running an osd on the same machine that has the /ceph mount?
There's known memory management problems with loopback network
filesystems; even NFS is known to trigger that. Using the kernel ceph
client to mount a ceph filesystem hosted on the same machine is not
safe.

A simple dd might not trigger the problems, because the kernel will
recognize the streaming write pattern and discard the pages early from
the buffer cache, but a full VM install isn't a clean streaming write.

-- 
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