Re: [Qemu-devel] The image size of instance VM keeps growing

[nicolas prochazka <prochazka.nicolas@gmail.com>]

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hello,
I think it's not qemu relative but windows relative
Windows do a lot of things as auto defrag disk ( without monitoring) when
idle time
read this document:
http://www.vmware.com/files/pdf/VMware-View-OptimizationGuideWindows7-EN.pdfand
optimize your guest.

Regards,
Nicolas P.

2012/5/23 Charles.Tsai-蔡清海-研究發展部 <charles.tsai@cloudena.com>

> Stefan,
>
>        Here are what we tested and found  for this issue.
>
>        1.      We checked the integrity of the qcow2 image by running
> “qemu-img check” and it looked good.
>        2.      We monitored the I/O activities of VM using
>        “Process monitor”, “Process explorer” and could not find a process
> running an aggressive I/O activity in the background.
>
>        In the guest OS, the following configurations are turn off to cut
> down I/O activities.
>        1.      Disable the NIC.
>        2.      Disable Windows automatic update.
>        3.      Disable the page file of the virtual memory.
>
>        After the VM ran for overnight, the image size for the running VM
> grew up to 3G bytes.
>
>
>        This issue is very easy to be duplicated. Here are the steps.
>
>        1.      Create a qcow2 image of 64-bit Windows 7 VM from the CD.
>        2.      Launch the VM
>        3.      Turn off the VM configurations stated above.
>        4.      Let the VM run.
>        5.      Watch the growth of the VM image size. The longer the VM
> runs, the bigger the size of the VM is.
>
>        During the run-time, you can run “process monitor” to watch guest
> OS’s I/O activities. You can see File I/O, registry I/O from the
>  system during the run-time in this test case. But the growth rate of the
> image size seems to be greater than default system I/O.
>
>
> -----Original Message-----
> From: Stefan Hajnoczi [mailto:stefanha@gmail.com]
> Sent: Monday, May 21, 2012 9:24 PM
> To: Charles.Tsai-蔡清海-研究發展部
> Cc: qemu-devel@nongnu.org; Jonah.Wu-吳君勉-研究發展部
> Subject: Re: [Qemu-devel] The image size of instance VM keeps growing
>
> On Mon, May 21, 2012 at 10:08 AM, Charles.Tsai-蔡清海-研究發展部
> <charles.tsai@cloudena.com> wrote:
> > We can run a tool to see if there is any active I/O or not. Does the
> image size shrink back if an I/O activity stops?
> > What we found here is that the image size kept growing. If this problem
> persists, it could eat up the entire disk space.
>
> It's possible for an image to grow larger than its backing file due to the
> layout and metadata of qcow2 (or any image file format).  But this overhead
> should be fixed to maximum 1 MB, maybe (assuming you are not using qcow2
> snapshots where the file can grow arbitrarily).
>
> If the image file is growing endlessly then there is a problem :).
> The starting point is figuring out which I/O request causes this to happen
> so it can be reproduced and debugged.  Can you isolate the problem to a few
> steps that can be reproduced?
>
> Stefan
>

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