Right away with FIO when carrying out random reads, we see much stronger 4-disk RAID performance using EXT4 and XFS with the Linux software RAID than out of the Btrfs RAID performance. To no surprise 4-disk RAID0 was the fastest (about the same IOPS on EXT4 and XFS) followed by RAID 6. EXT4 overall across the different RAID levels tended to perform better than XFS in this simple random read test.

Random writes were much faster at RAID0 and the single disk level than XFS, but XFS in turn was performing much better than Btrfs even though that file-system has various SSD optimizations.

The XFS and EXT4 RAID performance makes a whole lot more sense than the limited capabilities seen out of the native Btrfs RAID performance on this Linux 4.18.1 kernel.