The flavours of ZFS
- native ZFS in Solaris 11.
This is the Unix where ZFS was developped for. The most resource efficient and stable ZFS and propably the fastest one. In 20 years I have not seen as many bug reports up to dataloss than on Linux in a few weeks. Native ZFS is not free nor compatible to Open-ZFS. For noncommercial use/tests you can download Solaris 11 cbe for free (current Solaris beta)
- Open-ZFS 2.x
This is the ZFS in BSD, Linux, OSX and Windows. Due the marketshare of Linux, most Open-ZFS development happens here now, so this is mainstream ZFS. A few years ago, Illumos was upstream to Open-ZFS, now Open-ZFS is upstream to Illumos. Main problem here are the number of Linux distributions, each with a different Open-ZFS release or update policy. Checking issue tracker quite often is not a bad idea. For a backup pool it is a good idea to disable features to be less affected by bugs.
- Illumos ZFS
Illumos is the Opensource fork of Solaris. It inherits all of the Solaris advantages like stability, resource efficiency, easyness in handling, the Solaris iSCSI Comstar project or the in ZFS integrated kernelbased SMB server with a superiour integration of Windows ntfs alike ACL. Illumos is compatible to Open-ZFS 2.x but independent from Open-ZFS 2.x. It uses Open-ZFS now as upstream to integrate newer ZFS features after additional stability checks what makes it more stable than Open-ZFS. Illumos Issue tracker shows quite a similar low number of critical issues as Solaris.
Distributions are very close to Illumos (not as different as the many Linux distributions: NexentaStor (storage appliance), OmniOS (storage OS with a stable/long term stable), OpenIndiana (successor of OpenSolaris) or SmartOS (virtualizer OS, competitor to ESXi or Proxmox)