Am 04.09.2017 um 15:28 schrieb Timofey Titovets: > 2017-09-04 15:57 GMT+03:00 Stefan Priebe - Profihost AG > <s.pri...@profihost.ag>: >> Am 04.09.2017 um 12:53 schrieb Henk Slager: >>> On Sun, Sep 3, 2017 at 8:32 PM, Stefan Priebe - Profihost AG >>> <s.pri...@profihost.ag> wrote: >>>> Hello, >>>> >>>> i'm trying to speed up big btrfs volumes. >>>> >>>> Some facts: >>>> - Kernel will be 4.13-rc7 >>>> - needed volume size is 60TB >>>> >>>> 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. >>>> >>>> I can live with a data loss every now and and than ;-) so a raid 0 on >>>> top of the 4x radi5 is acceptable for me. >>>> >>>> Currently the write speed is not as good as i would like - especially >>>> for random 8k-16k I/O. >>>> >>>> My current idea is to use a pcie flash card with bcache on top of each >>>> raid 5. >>> >>> If it can speed up depends quite a lot on what the use-case is, for >>> some not-so-much-parallel-access it might work. So this 60TB is then >>> 20 4TB disks or so and the 4x 1GB cache is simply not very helpful I >>> think. The working set doesn't fit in it I guess. If there is mostly >>> single or a few users of the fs, a single pcie based bcacheing 4 >>> devices can work, but for SATA SSD, I would use 1 SSD per HWraid5. >> >> Yes that's roughly my idea as well and yes the workload is 4 users max >> writing data. 50% sequential, 50% random. >> >>> Then roughly make sure the complete set of metadata blocks fits in the >>> cache. For an fs of this size let's say/estimate 150G. Then maybe same >>> of double for data, so an SSD of 500G would be a first try. >> >> I would use 1TB devices for each Raid or a 4TB PCIe card. >> >>> You give the impression that reliability for this fs is not the >>> highest prio, so if you go full risk, then put bcache in write-back >>> mode, then you will have your desired random 8k-16k I/O speedup after >>> the cache is warmed up. But any SW or HW failure wil result in total >>> fs loss normally if SSD and HDD get out of sync somehow. Bcache >>> write-through might also be acceptable, you will need extensive >>> monitoring and tuning of all (bcache) parameters etc to be sure of the >>> right choice of size and setup etc. >> >> Yes i wanted to use the write back mode. Has anybody already made some >> test or experience with a setup like this? >> > > May be you can make work your raid setup faster by: > 1. Use Single Profile
I'm already using the raid0 profile - see below: 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. > 3. Use btrfs ssd_spread to decrease RMW cycles. Can you explain this? Stefan -- 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
