On Thu, 11 Sep 2014 06:48:31 +0200 Bostjan Skufca <bostjan@xxxxxx> wrote: > 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? I cannot guess what other people will assume. I certainly cannot guard against all possible incorrect assumptions. If you create an array which doesn't have true redundancy you will get a message from the kernel saying: %s: WARNING: %s appears to be on the same physical disk as %s. True protection against single-disk failure might be compromised. Maybe mdadm could produce a similar message... > > 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.) I really don't think there is any value is splitting a device into multiple partitions and putting more than one partition per device into an array. Have you tried using just one partition per device, making a RAID10 with --layout=f2 ?? NeilBrown > > > 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
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