>>> [ ... ] Currently without any ssds i get the best speed with: >>> - 4x HW Raid 5 with 1GB controller memory of 4TB 3,5" devices >>> and using btrfs as raid 0 for data and metadata on top of >>> those 4 raid 5. [ ... ] the write speed is not as good as i >>> would like - especially for random 8k-16k I/O. [ ... ]
> [ ... ] 64kb data stripe and 16kb parity Btrfs raid0 use 64kb > as stripe so that can make data access unaligned (or use single > profile for btrfs) 3. Use btrfs ssd_spread to decrease RMW > cycles. This is not a "revolutionary" scientific discovery as the idea of a working set of a small-size random-write workload, but it still takes a lot of "optimism" to imagine that it is possible to "decrease RMW cycles" for "random 8k-16k" writes on 64KiB+16KiB RAID5 stripes, whether with 'ssd_spread' or not. To "decrease RMW cycles" seems inded to me the better aim than following the "radical" aim of caching the working set of a random-small-write workload, but it may be less easy to achieve than desirable :-). http://www.baarf.dk/ -- 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
