I reported recently to the list there there's a performance problem with scrubs on raid5/6 pools, initial report and followups here: https://lore.kernel.org/linux-btrfs/CAHzMYBTXvY1VgcoFDUvc2NFmVKq2HJRHuS0VXzoneUMh79cySA@xxxxxxxxxxxxxx/ Quick recap: 4 disk raid5 (raid1 metadata) UUID: b75ee8b5-ae1c-4395-aa39-bebf10993057 Scrub started: Wed Nov 27 07:32:46 2019 Status: running Duration: 7:34:50 Time left: 1:52:37 ETA: Wed Nov 27 17:00:18 2019 Total to scrub: 1.20TiB Bytes scrubbed: 982.05GiB Rate: 36.85MiB/s Error summary: no errors found 11 disk raid5 (raid1 metadata) UUID: 1236acc8-dbd5-41bd-bf3d-872a8fbbce49 Scrub started: Sun Dec 15 11:23:45 2019 Status: running Duration: 0:51:34 Time left: 90:06:52 ETA: Thu Dec 19 06:22:13 2019 Total to scrub: 18.10TiB Bytes scrubbed: 175.12GiB Rate: 57.96MiB/s Error summary: no errors found Same 11 disk pool during a btrfs send to /dev/null confirming it's capable of much better read speeds: btrfs send /mnt/disks/Pics/T12_disk1_Pics_2019-12-15-0829/ | pv -bart > /dev/null At subvol /mnt/disks/Pics/T12_disk1_Pics_2019-12-15-0829/ 447GiB 0:13:19 [ 635MiB/s] [ 573MiB/s] Current speed 635MiB/s, average speed so far 573MiB/s
