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Re: [Qemu-devel] CoW image commit+shrink(= make_empty) support

From: Paolo Bonzini
Subject: Re: [Qemu-devel] CoW image commit+shrink(= make_empty) support
Date: Mon, 11 Jun 2012 10:01:15 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:12.0) Gecko/20120430 Thunderbird/12.0.1

Il 11/06/2012 09:59, Kevin Wolf ha scritto:
>>>>> >>>> I agree, doing it like mirroring for new writes on the top layer 
>>>>> >>>> makes
>>>>> >>>> sense, as long as you are willing to violate the (optional) speed
>>>>> >>>> parameter.  I wouldn't think violating the speed parameter in that 
>>>>> >>>> case
>>>>> >>>> would be an issue, as long as it is a documented affect of 
>>>>> >>>> performing a
>>>>> >>>> live commit on the active (top) layer.
>>> >> The question is what the speed parameter really means for a live commit
>>> >> block job (or for an active mirror). I think it would make sense to
>>> >> limit only the speed of I/O that doesn't come from the guest but is from
>>> >> the background copying.
>> > 
>> > Not necessarily, you can throttle the copying speed.  If the I/O from
>> > the guest has bursts, you will pick up the work later when the rate
>> > calms down.
> Then it's not an active mirror any more, but a passive one.

Yes, I guess what I was saying is that the passive mirror code can be
used also for live commit of the top image.


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