I get speeds 10-15 MB/s when writing to encrypted xfs. Even with no parity. Problem still there in safe mode.    The slow speed makes transferring files from windows computers almost unusable (explorer freezes and transfers stops until the data cached in ram is done writing to disk and that could take some time at 10MB/s).    Writing to unencrypted xfs gives me full speed.    Writing to encrypted btrfs (cache ssd raid1) gives me full speed (cache only share).