Re: [Qemu-devel] [RFC PATCH 1/1] ceph/rbd block driver for qemu-kvm

[MORITA Kazutaka]

At Fri, 21 May 2010 06:28:42 +0100,
Stefan Hajnoczi wrote:
> 
> On Thu, May 20, 2010 at 11:16 PM, Christian Brunner <address@hidden> wrote:
> > 2010/5/20 Anthony Liguori <address@hidden>:
> >> Both sheepdog and ceph ultimately transmit I/O over a socket to a central
> >> daemon, right?  So could we not standardize a protocol for this that both
> >> sheepdog and ceph could implement?
> >
> > There is no central daemon. The concept is that they talk to many
> > storage nodes at the same time. Data is distributed and replicated
> > over many nodes in the network. The mechanism to do this is quite
> > complex. I don't know about sheepdog, but in Ceph this is called RADOS
> > (reliable autonomic distributed object store). Sheepdog and Ceph may
> > look similar, but this is where they act different. I don't think that
> > it would be possible to implement a common protocol.
> 
> I believe Sheepdog has a local daemon on each node.  The QEMU storage
> backend talks to the daemon on the same node, which then does the real
> network communication with the rest of the distributed storage system.

Yes.  It is because Sheepdog doesn't have a configuration about
cluster membership as I mentioned in another mail, so the drvier
doesn't know which node to access other than localhost.

>  So I think we're not talking about a network protocol here, we're
> talking about a common interface that can be used by QEMU and other
> programs to take advantage of Ceph, Sheepdog, etc services available
> on the local node.
> 
> Haven't looked into your patch enough yet, but does librados talk
> directly over the network or does it connect to a local daemon/driver?
> 

AFAIK, librados access directly over the network, so I think it is
difficult to define a common interface.


Thanks,

Kazutaka