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Hi All,

I have a cluster of three nodes set up.  Live migration is accomplished via
an NFS mount over 10GigE shared by all three nodes.

I have noticed that when a VM is brand new I am getting close to 60MB/s
disk write when using "dd if=/dev/zero of=file bs=1M count=1k
conv=fdatasync". after doing this 10s of times the perfomance of the disk
seems to drop  to around 4 - 12 MB/s.

I have also noticed that doing a live-migration causes a similar effect
immediately.

Here is the virsh xml output of one of my VMs:
https://gist.github.com/swinchen/397fbe3bb74305064944

I have read several "tuning" guides and most of the suggestions seems to be
configured already (cache='none', virtio for network, disk and memballoon).


Do you think qcow2 is causing my issue and if so is there a way to boot an
instance and override the disk format?

Thanks,
Sam
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