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Re: [Qemu-devel] [RFC] qmp interface for save vmstate to image
From: |
Kevin Wolf |
Subject: |
Re: [Qemu-devel] [RFC] qmp interface for save vmstate to image |
Date: |
Mon, 18 Mar 2013 10:04:30 +0100 |
User-agent: |
Mutt/1.5.21 (2010-09-15) |
Am 18.03.2013 um 07:40 hat Wenchao Xia geschrieben:
> δΊ 2013-3-15 22:51, Stefan Hajnoczi ει:
> > On Fri, Mar 15, 2013 at 03:24:38PM +0800, Wenchao Xia wrote:
> >> I'd like to add a new way to save vmstate, which will based on the
> >> migration thread, but will write contents to block images, instead
> >> of fd as stream. Following is the method to add API:
> >
> > Hi Wenchao,
> > What use cases are there besides saving vmstate to a raw image?
> >
> > I'm curious if you're proposing this since there is no "file:" URI or
> > because you really want to do things like saving vmstate into a qcow2
> > file or over NBD.
> >
> > Stefan
> >
> Hi, Stefan
> Most used cases would be "raw" and "qcow2", which is flex and can be
> chosen by user. In this way, existing block layer feature in qemu can
> be used, such as tagging zeros. I haven't check the buffer/cache status
> in qemu block layer, but if there is, it can also benefit.
> User can specify "raw" or "qcow2" according to host configuration, If
> there is dedicated storage components underlining, he can use "raw" to
> skip qemu's block layer.
Oh, seems I misread this then. I thought this was about internal live
snapshots, which is a feature that I consider really useful. I'm not so
sure if saving the VM state as the disk contents of a qcow2 image is
really helpful.
If zero clusters help a lot, then there's clearly something to improve
in the migration protocol, because it shouldn't send so many zeros in
the first place.
Kevin
Re: [Qemu-devel] [RFC] qmp interface for save vmstate to image, Pavel Hrdina, 2013/03/18