I've tested ZFS, and it was terrible, buggy, slow, unreliable, and very quickly just destroyed itself. Despite having the letter "Z" in the name, its basically unreliable crap. btrfs, on the other hand, seems to actually work quite well.
ZFS looks pretty unusable to me. That was ZFS-FUSE though, so its performance was as slow as NTFS (FUSE). Nobody could ever get any serious productivity using that as a primary FS. I'd give the native stuff a try, but so far there's still nothing better than JFS...
What on Earth? The Illumos folks are developing ZFS out in the open and its receiving new features all the time. Oracle are continuing their closed version, but Illumos has broken compatibility with that and is taking ZFS where they want it to go. Nothing dead about it at all.
Also, anyone with past bad experiences, give the native ZFSonLinux another try if you can - it's come on an awfully long way in the last year!
The premise of ZFS is scalability, manageability, stability, data security, and features.
ZFS would be great as a NAS, a media server (with big files such as movies), and file system for backup and archival.
And FUSE's module performance != native kernel module performance
And that if we talk about non-tuned-for-specific-workload kind of performance.
If you can spend on a SSD or two, you could use them as cache and/or ZIL devices ... and/or the natural raid setup with ZFS, which simply outperforms whatever black magic you can do on top of a "primitive" filesystem like ext4
Again, ZFS is not intended for low-end desktop computers (think: ZFS for normal full operation needs at least 4GB .. with an optimal "start" of 8GB) ... so it's basically bogus to compare it against ext4 and worst: in the desktop land (where ZFS has little to offer compared to what it requires, and where it doesn't aim)
Is more reasonable to compare it against something of similar kind, like btrfs.
But on the areas of NAS, Storage providers, and other kinds of servers who could benefit of features like dedupe or transparent compression and/or you have some gear in there ... you win, in a manner that cannot be expressed
For the last use cases, at least, SnapRAID is at least as good of a solution as ZFS, plus there is nearly zero chance that you will lose your entire array since it doesn't stripe the data (it does something more like the old WHS Spaces or Unraid where they set aside disks to hold parity).
Btrfs will be tested enough when Oracle itself will approve it for their database. Fedora is RH testing playground, so they don't care if you loose all your data.