Re: [Qemu-devel] [PATCH v4 3/6] add backup related monitor commands

[Stefan Hajnoczi]

On Sun, Mar 10, 2013 at 10:32 AM, Dietmar Maurer <address@hidden> wrote:
>> >> What I am looking for is a stripped down patch series with just a
>> >> backup block job (no backup archive writer or migration code).  That
>> >> would be easily merged and saves you front rebasing this series as QEMU
>> changes.
>> >
>> > That is Patch 2/6?
>>
>> Yes.  I sent an RFC series that shows this approach.  It is just a prototype 
>> but it
>> demonstrates that the NBD approach works and performs reasonably well for a
>> quick Python hack.
>>
>> The stripped down patch series needs:
>> 1. (Optional) query-block virtual_size field if management tool needs to 
>> query
>> drive size 2. Patch 2/6 with review comments addressed 3. 'block-backup' QMP
>> command (and optionally HMP command)
>>
>> That's it!
>
> Thanks. I also have an  implementation here using that approach (using nbd.c).
> The problem is the performance you get. 28% delay is not acceptable.
>
> In fact, I want to have the fastest possible solution (additional delay = 0).
>
> You want to move the code out of qemu, so that management frameworks
> can easily plug their own backup tools. That is perfectly valid, but we 
> should do
> it in a way that does not influence performance.
>
> So are there any other ideas?

Same discussion in the other thread, so let's move there where we both
just posted.

Stefan