On 05/24/2010 10:12 AM, MORITA Kazutaka wrote:
At Sun, 23 May 2010 15:01:59 +0300,
Avi Kivity wrote:
On 05/21/2010 12:29 AM, Anthony Liguori wrote:
I'd be more interested in enabling people to build these types of
storage systems without touching qemu.
Both sheepdog and ceph ultimately transmit I/O over a socket to a
central daemon, right?
That incurs an extra copy.
So could we not standardize a protocol for this that both sheepdog and
ceph could implement?
The protocol already exists, nbd. It doesn't support snapshotting etc.
but we could extend it.
I have no objection to use another protocol for Sheepdog support, but
I think nbd protocol is unsuitable for the large storage pool with
many VM images. It is because nbd protocol doesn't support specifing
a file name to open. If we use nbd with such a storage system, the
server needs to listen ports as many as the number of VM images. As
far as I see the protocol, It looks difficult to extend it without
breaking backward compatibility.
The server would be local and talk over a unix domain socket, perhaps
anonymous.
nbd has other issues though, such as requiring a copy and no support for
metadata operations such as snapshot and file size extension.
--
Do not meddle in the internals of kernels, for they are subtle and quick to
panic.
