Am Wed, 6 Jul 2016 13:20:15 +0100 schrieb Tomasz Kusmierz <tom.kusmi...@gmail.com>:
> When I think of it, I did move this folder first when filesystem was > RAID 1 (or not even RAID at all) and then it was upgraded to RAID 1 > then RAID 10. Was there a faulty balance around August 2014 ? Please > remember that I’m using Ubuntu so it was probably kernel from Ubuntu > 14.04 LTS > > Also, I would like to hear it from horses mouth: dos & donts for a > long term storage where you moderately care about the data: RAID10 - > flaky ? would RAID1 give similar performance ? The current implementation of RAID0 in btrfs is probably not very optimized. RAID0 is a special case anyways: Stripes have a defined width - I'm not sure what it is for btrfs, probably it's per chunk, so it's 1GB, maybe it's 64k **. That means your data is usually not read from multiple disks in parallel anyways as long as requests are below stripe width (which is probably true for most access patterns except copying files) - there's no immediate performance benefit. This holds true for any RAID0 with read and write patterns below the stripe size. Data is just more evenly distributed across devices and your application will only benefit performance-wise if accesses spread semi-random across the span of the whole file. And at least last time I checked, it was stated that btrfs raid0 does not submit IOs in parallel yet but first reads one stripe, then the next - so it doesn't submit IOs to different devices in parallel. Getting to RAID1, btrfs is even less optimized: Stripe decision is based on process pids instead of device load, read accesses won't distribute evenly to different stripes per single process, it's only just reading from the same single device - always. Write access isn't faster anyways: Both stripes need to be written - writing RAID1 is single device performance only. So I guess, at this stage there's no big difference between RAID1 and RAID10 in btrfs (except maybe for large file copies), not for single process access patterns and neither for multi process access patterns. Btrfs can only benefit from RAID1 in multi process access patterns currently, as can btrfs RAID0 by design for usual small random access patterns (and maybe large sequential operations). But RAID1 with more than two disks and multi process access patterns is more or less equal to RAID10 because stripes are likely to be on different devices anyways. In conclusion: RAID1 is simpler than RAID10 and thus its less likely to contain flaws or bugs. **: Please enlighten me, I couldn't find docs on this matter. -- Regards, Kai Replies to list-only preferred. -- 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
