On 12/03/13 09:48, Sylvain Bauza wrote: > Long lasting bug and huge update, but I think I got the root cause. > FYI, Windows 2003 is having a write cache enabled by default on disk > drivers. Even with virtio (see driver details, policies). Hi there, That option did you use in driver policy? Thanks > > As a consequence, any DLL which is open could be corrupted if we try a > simple 'qemu-img convert' against the VM. > The proper way to do a live snapshot is to disable the writecache (and > goodbye good perfs!) and do the convert. > The other way is to stop the VM, perform a 'qemu-img snapshot', then > convert the snapshot. > > Hope it can help other people. > -Sylvain > > > Le 14/02/2013 11:11, Sylvain Bauza a écrit : >> Interesting point you mention. Even if qcow2 is read only, the image >> is changing (especially, I'm running IIS with ASP support and VB >> DLLs) while the snapshot is taken. >> >> As asked in a second post, I'm running with latest Windows virtio >> drivers, but I only apply a virtio driver update *after* running an >> instance, not before taking the snapshot. >> >> What I'll try : run an instance, update the driver, stop the >> instance, do a qemu-img convert once the instance is stopped. >> >> >> Le 14/02/2013 09:15, Stefan Hajnoczi a écrit : >>> On Wed, Feb 13, 2013 at 10:53:14AM +0100, Sylvain Bauza wrote: >>>> As per documentation, Nova (Openstack Compute layer) is doing a >>>> 'qemu-img convert -s' against a running instance. >>>> http://docs.openstack.org/trunk/openstack-compute/admin/content/creating-images-from-running-instances.html >>>> >>> That command will not corrupt the running instance because it opens the >>> image read-only. >>> >>> It is possible that the new image is corrupted since qemu-img is >>> reading >>> from a qcow2 file that is changing underneath it. However, the chance >>> is small as long as the snapshot isn't deleted while qemu-img >>> convert is >>> running. >>> >>> So this doesn't sound like the cause of the problems you are seeing. >>> >>> Stefan >> > > -- > To unsubscribe from this list: send the line "unsubscribe kvm" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
