On Wed, Aug 14, 2013 at 10:40:06AM +0800, Fam Zheng wrote: > On Tue, 08/13 16:13, Spensky, Chad - 0559 - MITLL wrote: > > Hi All, > > > > I'm working with some disk introspection on KVM, and we trying to create > > a shadow image of the disk. We've hooked the functions in block.c, in > > particular bdrv_aio_writev. However we are seeing writes go through, > > pausing the VM, and the comparing our shadow image with the actual VM > > image, and they aren't 100% synced up. The first 1-2 sectors appear to be > > always be correct, however, after that, there are sometimes some > > discrepancies. I believe we have exhausted most obvious bugs (malloc > > bugs, incorrect size calculations etc.). Has anyone had any experience > > with this or have any insights? > > > > Our methodology is as follows: > > 1. Boot the VM. > > 2. Pause VM. > > 3. Copy the disk to our shadow image. > > How do you copy the disk, from guest or host? > > > 4. Perform very few reads/writes. > > Did you flush to disk? > > > 5. Pause VM. > > 6. Compare shadow copy with active vm disk. > > > > And this is where we are seeing discrepancies. Any help is much > > appreciated! We are running on Ubuntu 12.04 with a modified Debian build. > > > > - Chad > > > > -- > > Chad S. Spensky > > > > I think drive-backup command does just what you want, it creates a image > and copy-on-write date from guest disk to the target, without pausing > VM. Or perhaps drive-mirror. Maybe Chad can explain what the use case is. There is probably an existing command that does this or that could be extended to do this safely. 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
