Thanks for you reply,

On 06/08/2015 12:31 PM, Andrey Korolyov wrote:
On Mon, Jun 8, 2015 at 1:24 PM, Arnaud Virlet <avir...@easter-eggs.com> wrote:
Hi

Actually we use libvirt VM with ceph rbd pool for storage.
By default we want to have "disk cache=writeback" for all disks in libvirt.
In /etc/ceph/ceph.conf, we have "rbd cache = true" and for each VMs XML we
set "cache=writeback" for all disks in VMs configuration.

We want to use one ocfs2 volume on our rbd pool. For this volume we want set
cache=none. When we set cache=none in libvirt template for this hosts, it
doesn't work.

Can you please describe this more specifically? Does the libvirt
produce a launch string with cache=none or you are measuring the cache
(mis)presence in some other way? The rbd_cache setting and cache=xxx
for qemu should show a conjugate behavior.

With rbd_cache = true in ceph.conf and cache = none in XML, Libvirt produce a launch string with cache=none for the ocfs2 volume.

The only way that's work  is when we set "rbd cache = false" in
/etc/ceph/ceph.conf.

How can I set cache=none just for one volume specifically without modifing
default settings in ceph.conf?


Regards,

Arnaud
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