BtrFS is still an ongoing project for me, but if it will become a production platform for me soon is the question. Also playing with mirroring on BtrFS level made me wonder even more as it does the calculating about storage usage a little bit differently. Normally with mirroring you see the storage you can allocate and has been allocated. With BtrFS you see the total amount of data available on all disks combined as show in the example below.
$ sudo btrfs filesystem df /mnt Data, RAID1: total=5.98GB, used=5.36GB System, RAID1: total=8.00MB, used=4.00KB System: total=4.00MB, used=0.00 Metadata, RAID1: total=256.00MB, used=6.01MB $ df -h /mnt Filesystem Size Used Avail Use% Mounted on /dev/mapper/vg01-btrfsm1 16G 11G 4.8G 70% /mnt
I really like ZFS, but I really wonder if BtrFS could replace it. For now I see too many drawbacks in how BtrFS has been implemented and how distributions may use it. Maybe when Debian 8 is in testing it may be a better time to give BtrFS another chance, but swap space and encrypted file systems are still problems that need to be tackled.