[etbe]

In the post I wrote 'between the 2 SSDs SMART reports 18 uncorrectable errors and “btrfs device stats” reports 55 errors on one of them'. That's 37 errors that BTRFS found that mdadm wouldn't have found. 37 errors out of 500G of data isn't a lot, but it depends where it occurs, if it's in the root directory then it will mess up your day (annoyingly BTRFS doesn't track where the errors were so you can't easily determine what the implications of not having BTRFS might be). That is not unusual, I have had similar things on almost all my systems that run BTRFS or ZFS.

Also I use snapshots too.