Re: [Qemu-devel] [RFC] Replication agent requirements (was [RFC PATCH] replication agent module)

[Anthony Liguori]

On 02/08/2012 07:00 AM, Ori Mamluk wrote:
> Hi,
> Following previous mails from Kevin and Dor, I'd like to specify the high level
> requirements of a replication agent as I see them.
>
> 1. Report each write to a protected volume to the rephub, at an IO transaction
> granularity
> * The reporting is not synchronous, i.e. the write completion is not delayed
> until the rephub received it.
> * The IOs have to be the raw guest IOs - i.e. not converted to any sparse format
> or another filter that alters the size/offset

For now.  I'm sure you'll eventually have a synchronous replication requirement.

We're doomed to reinvent all of the Linux storage layer it seems.  I think we 
really only have two choices: make better use of kernel facilities for this 
(like drbd) or have a proper, pluggable, storage interface so that QEMU proper 
doesn't have to deal with all of this.

Gluster is appealing as a pluggable storage interface although the license is 
problematic for us today.

I'm quite confident that we shouldn't be in the business of replicating storage 
though.  If the answer is NBD++, that's fine too.

Regards,

Anthony Liguori