I have been using Ubuntu + LXD + RaidZ for as long as it was available. Recently (a year ago?) I first had noticed some kind of unclear performance issue with a FLEX container. Heavy file streaming/download would hose and make entire server unusable. I had no idea what to do, and I pretty much randomly converted the LXD storage to BTRFS, and everything was fine. Last few months I ran into same problem with a bunch of PostgreSQL containers doings lots of writes, and same solution helped. Not sure if it's a ZFS problem or LXD, but I will not use ZFS in high load scenario again.
