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

[Michael Roth <mdroth@linux.vnet.ibm.com>]

On Mon, May 21, 2012 at 07:47:49AM +0000, Charles.Tsai-蔡清海-研究發展部 wrote:
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> We created a qcow2 based-image for a VM whose size is big when it is created. When a VM is launched, it is a instance VM image which refers to the based-image. Initially, the image size of instance VM is smaller than that of the based-mage. But we found the image size of the instance VM kept growing, when a VM ran in idle state. We doubted this issue is caused by the Windows swap file(virtual memory) that Windows OS pages the memory contents to it during the run-time. We did disable the swap file setting from Windows but the image size of the instance VM still kept growing.
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> Ideally, the image size of instance VM is supposed to remain in a smaller size than the based-image. Why does it keep growing in size which is even bigger than that of based-image? Our VM, in fact, did nothing during the idle state.
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Do you have automatic indexing turned on in the guest? Not sure of the
specifics WRT to NTFS, but indexing might be causing metadata updates
(particularly last access time) that might be causing a COW on a lot of
blocks in a relatively short amount of time.