Re: [Qemu-devel] [RFC PATCH] replication agent module

[Paolo Bonzini]

On 02/07/2012 03:48 PM, Ori Mamluk wrote:
> > The current streaming code in QEMU only deals with the former.
> > Streaming to a remote server would not be supported.
> I need it at the same time. The Rephub reads either the full volume or
> parts of, and concurrently protects new IOs.

Why can't QEMU itself stream the full volume in the background, and send 
that together with any new I/O?  Is it because the rephub knows which 
parts are out-of-date and need recovery?  In that case, as a first 
approximation the rephub can pass the sector at which streaming should 
start.

But I'm also starting to wonder whether it would be simpler to use 
existing replication code.  DRBD is more feature-rich, and you can use 
it over loopback or NBD devices (respectively raw and non-raw), and also 
store the replication metadata on a file using the loopback device. 
Ceph even has a userspace library and support within QEMU.

Paolo