Comment 5 for bug 1422307

I succeeded to reproduce the bug without NBD:

$ ./qemu-img create -f vdi test.vdi 2G
Formatting 'test.vdi', fmt=vdi size=2147483648 static=off
$ ./qemu-img create -f raw test.raw 2G
Formatting 'test.raw', fmt=raw size=2147483648
$ x86_64-softmmu/qemu-system-x86_64 -enable-kvm -drive if=virtio,file=blkverify:test.raw:test.vdi,format=raw -drive if=virtio,file=data.img,format=raw,format=raw -cdrom ~/tmp/arch.iso -m 512 -boot d
blkverify: read sector_num=810976 nb_sectors=256 contents mismatch in sector 811008

Operations in the guest:
$ dd if=/dev/vdb of=/dev/vda
$ dd if=/dev/vda of=/dev/null

So it really looks like something's broken in qemu's VDI block driver.

Max