On Sat, Mar 12, 2016 at 05:04:16PM +0200, Nir Soffer wrote:
> On Sat, Mar 12, 2016 at 1:55 PM, Samuli Heinonen <samp...@neutraali.net> 
> wrote:
> > Hello all,
> >
> > It seems that oVirt 3.6 is still using FUSE to access GlusterFS storage 
> > domains instead of using QEMU driver (libgfapi). As far as I know libgfapi 
> > support should be available in Libvirt and QEMU packages provided in CentOS 
> > 7.
> We started to work this during 3.6 development, but the work was
> suspended because
> libvirt and qemu do not support multiple gluster servers [1]. This
> means that if your single
> server is down, you will not be able to connect to gluster.
> Recently Niels suggested that we use DNS for this purpose - if the DNS
> return multiple
> servers, libgafpi should be able to failover to one of these servers,
> so connecting with
> single server address should good as multiple server support in libvirt or 
> qemu.

And in case the local oVirt Node is part of the Gluster Trusted Storage
Pool (aka running GlusterD), qemu can use "localhost" to connect to the
storage too. It is only the initial connection that would benefit from
the added fail-over by multiple hosts. Once the connection is
established, qemu/libgfapi will connect to all the bricks that
participate in the volume. That means that only starting or attaching a
new disk to a running VM is impacted when the gluster:// URL is used
with a storage server that is down. In case oVirt/VDSM knows what
storage servers are up, it could even select one of those and not use a
server that is down.

I've left a similar note in [1], maybe it encourages to start with a
"single host" solution. Extending it for multiple hostnames should then
be pretty simple, and it allows us to start furter testing and doing
other integration bits.

And in case someone cares about (raw) sparse files (not possible over
FUSE, only with Linux 4.5), glusterfs-3.8 will provide a huge
improvement. A qemu patch for utilizing it is under review at [4].


> The changes needed to support this are not big as you can see in [2],
> [3]. However the work
> was not completed and I don't know if it will completed for 4.0.
> > Is there any workarounds how to use libgfapi with oVirt before it’s
> > officially available?
> I don't know about any.
> [1] https://bugzilla.redhat.com/1247521
> [2] https://gerrit.ovirt.org/44061
> [3] https://gerrit.ovirt.org/33768

[4] http://lists.nongnu.org/archive/html/qemu-block/2016-03/msg00288.html

> Nir

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