On 11 September 2014 02:31, NeilBrown <neilb@xxxxxxx> wrote: > On Wed, 10 Sep 2014 23:24:11 +0200 Bostjan Skufca <bostjan@xxxxxx> wrote: >> What does "properly" actually mean? >> I was doing some benchmarks with various raid configurations and >> figured out that the order of devices submitted to creation command is >> significant. It also makes raid10 created in such mode reliable or >> unreliable to a device failure (not partition failure, device failure, >> which means that two raid underlying devices fail at once). > > I don't think you've really explained what "properly" means. How exactly do > you get better throughput? > > If you want double-speed single-thread throughput on 2 devices, then create a > 2-device RAID10 with "--layout=f2". I went and retested a few things and I see I must have done something wrong before: - regardless whether I use --layout flag or not, and - regardless of device cli arg order at array creation time, = I always get double-speed single-thread throughput. Yaay! Anyway, the thing is that regardless of -using -layout=f2 or not, redundancy STILL depends on the order of command line arguments passed to mdadm --create. If I do: - "sda1 sdb1 sda2 sdb2" - redundandcy is ok - "sda1 sda2 sdb1 sdb2" - redundancy fails Is there a flag that ensures redundancy in this particular case? If not, don't you think the naive user (me, for example) would assume that code is smart enough to ensure basic redundancy, if there are at least two devices available? Because, if someone wants only performance and no redundancy, they will look no further than raid 0. But raid10 strongly hints at redundancy being incorporated in it. (I admit this is anecdotal, based on my own experience and thought flow.) b. -- 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
