2017-09-04 21:32 GMT+03:00 Stefan Priebe - Profihost AG <s.pri...@profihost.ag>: >> May be you can make work your raid setup faster by: >> 1. Use Single Profile > > I'm already using the raid0 profile - see below:
If i understand correctly, you have a very big data set with random RW access, so: I'm saying about single profile for compact writes to one device, that can make WB cache more effective Because writes will not spread on several devices and as result that increase chance that full stripe will be overwriten That's will just work as raid0 with very big stripe size. > Data,RAID0: Size:22.57TiB, Used:21.08TiB > Metadata,RAID0: Size:90.00GiB, Used:82.28GiB > System,RAID0: Size:64.00MiB, Used:1.53MiB > >> 2. Use different stripe size for HW RAID5: >> i think 16kb will be optimal with 5 devices per raid group >> That will give you 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) > > That sounds like an interesting idea except for the unaligned writes. > Will need to test this. Afaik btrfs also use 64kb for metadata: https://github.com/torvalds/linux/blob/e26f1bea3b833fb2c16fb5f0a949da1efa219de3/fs/btrfs/extent-tree.c#L6678 >> 3. Use btrfs ssd_spread to decrease RMW cycles. > Can you explain this? Long description: https://www.spinics.net/lists/linux-btrfs/msg67515.html Short: that option will change allocator logic. Allocator will spread writes more aggressively and always try write to new/empty area. So in theory that will write new data to new empty chunk, so if you have much free space that will make some guaranty to not touch old data, so not do RWM and in theory always do full stripe write. But if you expect that you array will be near full and you don't want do defragment on that, that can easy get you enospace error. > Stefan That just my IMHO, Thanks. -- Have a nice day, Timofey. -- 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
