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

[Stefan Hajnoczi <stefanha@gmail.com>]

On Thu, May 20, 2010 at 11:16 PM, Christian Brunner <chb@muc.de> wrote:
> 2010/5/20 Anthony Liguori <anthony@codemonkey.ws>:
>> 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.
 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?

Stefan