On Fri, 22 Jul 2011 18:10:33 +0900 Namhyung Kim <namhyung@xxxxxxxxx> wrote: > NeilBrown <neilb@xxxxxxx> writes: > > > RAID6 is only allowed to choose 'reconstruct-write' while RAID5 is > > also allow 'read-modify-write' > > Apart from this difference, handle_stripe_dirtying[56] are nearly > > identical. So resolve these differences and create just one function. > > > > Signed-off-by: NeilBrown <neilb@xxxxxxx> > > Reviewed-by: Namhyung Kim <namhyung@xxxxxxxxx> > > BTW, here is a question: > Why RAID6 doesn't allow the read-modify-write? I don't think it is > not possible, so what prevents doing that? performance? complexity? > or it's not possible? Why? :) The primary reason in my mind is that when Peter Anvin wrote this code he didn't implement read-modify-write and I have never seen a need to consider changing that. You would need a largish array - at least 7 devices - before RWM could possibly be a win, but some people do have arrays larger than that. The computation to "subtract" from the Q-syndrome might be a bit complex - I don't know. Peter: maybe you have a reason that I haven't mentioned? Thanks, NeilBrown -- To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
