[ ... ] >>>> Case #1 >>>> 2x 7200 rpm HDD -> md raid 1 -> host BTRFS rootfs >>>> -> qemu cow2 storage -> guest BTRFS filesystem >>>> SQL table row insertions per second: 1-2
>>>> Case #2 >>>> 2x 7200 rpm HDD -> md raid 1 -> host BTRFS rootfs >>>> -> qemu raw storage -> guest EXT4 filesystem >>>> SQL table row insertions per second: 10-15 [ ... ] >> Q 0) what do you think that you measure here? > Cow's fragmentation impact on SQL write performance. That's not what you are measuring, you are measing the impact on speed of configurations "designed" (perhaps unintentionally) for maximum flexibility, lowest cost, and complete disregard for speed. [ ... ] > It was quick and dirty task to find, prove and remove > performance bottleneck at minimal cost. This is based on the usual confusion between "performance" (the result of several tradeoffs) and "speed". When you report "row insertions per second" you are reporting a rate, that is a "speed", not "performance", which is always multi-dimensional. http://www.sabi.co.uk/blog/15-two.html?151023#151023 In the cases above speed is low, but I think that, taking into account flexibility and cost, performance is pretty good. > AFAIR removing storage cow2 and guest BTRFS storage gave us ~ > 10 times boost. "Oh doctor, if I stop stabbing my hand with a fork it no longer hurts, but running while carrying a rucksack full of bricks is still slower than with a rucksack full of feathers". [ ... ] -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
