On Mon, Jul 30, 2012 at 9:10 PM, Mark Moseley <moseleymark@xxxxxxxxx> wrote: > While I might've answered my own question, I'm no fio expert. I don't > necessarily trust that I'm testing it correctly, which is why I'm > asking here. Running the same test multiple times gives me > 30-40meg/sec for both read and write on the > preallocation=metadata-derived image, vs 0.5-1meg/sec for > non-preallocation=metadata-derived images, both which sound way too > high/low to be right. Same box (ubuntu 12.04 64-bit, running the stock > ubuntu qemu 1.0), same disk, even the same directory. I could also see > some bizarre side effect happening that I'm not aware of, ready to > bite me later on down the road, like, say, that it's silently actually > reading/writing the original image (just a made-up example). qemu-devel@xxxxxxxxxx is the best place to discuss QEMU image formats. The development of qcow2 happens there. Your fio question can't be answered without the job file. Please post it. I agree that the numbers look weird, the difference is too great. Are you using -drive ...,cache=none on your qemu command-line and "direct=1" or "buffered=0" (they are synonyms) in the fio job file? Those are necessary to take the host and guest page caches out of the equation. 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
