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

From: Charles . Tsai-蔡清海-研究發展部
Subject: Re: [Qemu-devel] The image size of instance VM keeps growing
Date: Thu, 24 May 2012 10:40:43 +0000


        Can you explain why a 64KB could be allocated for each sector write?

        Right now, I am testing a VM with 8G virtual disk space.
        The disk only has 12.6 MB free space left when I run the test.
        I am going to see what will happen in this test case.

-----Original Message-----
From: Stefan Hajnoczi [mailto:address@hidden 
Sent: Wednesday, May 23, 2012 8:57 PM
To: Charles.Tsai-蔡清海-研究發展部
Cc: address@hidden; Jonah.Wu-吳君勉-研究發展部
Subject: Re: [Qemu-devel] The image size of instance VM keeps growing

On Wed, May 23, 2012 at 11:47 AM, Charles.Tsai-蔡清海-研究發展部
<address@hidden> wrote:
>        After the VM ran for overnight, the image size for the running VM grew 
> up to 3G bytes.

What is the size of the backing file?  3G is small for a Windows guest.  Any 
sector that is written to could cause 64 KB to be allocated in the image file.

If qemu-img check sees no inconsistencies then it seems the guest is writing to 
previously untouched regions of the disk...causing the
qcow2 to grow.

However, the qcow2 file should not grow much beyond its virtual disk size.  So 
if you find the qcow2 is 3G but the virtual disk size is 1G, then there is a 
bug.  But from what you've posted so far I suspect the guest is simply writing 
to the disk.


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