I'm not having nearly your experience but I just want to say I'm agreeing 100% to you conclusions based on my experience. We ran at Uni a Hadoop Cluster that ha

I'm not having nearly your experience but I just want to say I'm agreeing 100% to you conclusions based on my experience. We ran at Uni a Hadoop Cluster that had disks slowly dying (some bad sectors every few days, but otherwise fine) and lacked the money to replace them. We replaced ext4 with ZFS (no raid, just plain zpools with failmode=continue) and ZFS ran mostly fine and scrubs kept the metadata sane. Never had data loss (HDFS has it's own replication and checksumming, we just need sane metadata for Hadoop to run and intermediate MapReduce outputs where send to directories with zfs set copies=2) and we only replaced the botched disks that had longer scrub times or couldn't survive a scrub. I'm still surprised how ZFS managed to pull that off. Only bugs I've found where related to ZoL at this time but could be worked around. btrfs switched to readonly as fast as ext4 (which is probably the correct thing to do) but was useless for this problem. On new hardware with new enterprise disks we choose btrfs and we had a painful tour of crashes, data corruption, metadata corruption (undeletable files), deadlocks until kernel 4.4 where things got a little bit better. Here disks and server where enterprise class and fully working. Just btrfs bugs. Also no RAID. I'm not doing that anymore so I don't know if any new bugs appeared but the whole experience will keep me from ever using btrfs. This was ~2years ago and you could easily find lot's of slides Fujitsu or Suse that btrfs is stable and you can use it (around kernel 3.13-3.16). It's probably fine for your notebook or even your backup HDD but don't think you can stress it without experiencing pain (be it corruption, hangups or dataloss) or just abysmal performance. That beeing said ZFS on Linux is also a far cry from rock solid but I'm optimistic that they flesh out the problems and tackle them in a solid way. As a Linux fanboy for years this gave me some solid appreciation for Solaris engineering.