zfs can sort of grow by adding vdevs, as you say, however it's pretty wasteful due to the new parity drives It was much more efficient to expand the mdraid raid

zfs can sort of grow by adding vdevs, as you say, however it's pretty wasteful due to the new parity drives It was much more efficient to expand the mdraid raid 6 and expand the btrfs onto that. The other backup server does use zfs (albeit the user mode fuse version). I set up that system in a similar way putting zfs-fuse on mdraid 6.