On 10/05/2015 18:02, Stefan Weil wrote: >> Since the default qemu-img convert case isn't slowed down, I >> would think that correctness trumps performance. Nevertheless, >> it's a huge difference. > > I doubt that the convert case isn't slowed down.
The *default* convert case isn't slowed down because "qemu-img convert" defaults to the "unsafe" cache mode. The *non-default* convert case with flushes was slowed down indeed: 2x in total (if you include the final flush done by bdrv_close), and 10x if you only consider the sequential write part of convert. Paolo > Writing to a tmpfs as it was obviously done for the test is not a > typical use case. > With real hard disks I expect a significant slowdown. > > Stefan
