Why ZFS's CDDL license matters for ZFS on Linux
In a G+ conversation about ZFS I read the following:
[...] so, why use BTRFS at all? :-) Just the fact that it's GPL (and so able to be embedded into the kernel source tree) doesn't seem enough, specially considering that CDDL (the ZFS license) is a bona fide open source license, [...]
On the whole I like ZFS on Linux, but let's not mince words here: this licensing issue is a big issue. Were btrfs and ZFS close to general parity, it would be a very strong push towards btrfs.
That ZFS is CDDL licensed means that it can never be included in the Linux kernel source. It may mean that it can't be prepackaged in binary form by distributions, or at least by distributions that care strongly about licensing issues. The CDDL is part of what makes it extremely unlikely that Red Hat Enterprise or Ubuntu LTS will ever officially support ZoL, making it always be a 'batteries not included, you get to integrate it' portion of the system.
That ZFS will not be included in the Linux kernel source (because of the CDDL among other reasons) means that you are more at risk of developers ceasing to update ZFS for newer kernels (among other less important effects).
(Being in the Linux kernel source is no guarantee that code will be maintained, but it increases the chances a fair bit.)
These are risks that we'd be willing and able to take on, so they aren't real obstacles for us using ZoL if that turns out to be the best option for new fileservers. But they still weigh on my mind and there are any number of places where they are going to be real issues, sometimes killer ones.
(I've written about this before.)
(Given the current situation with 4k disks, we're already looking at recreating pools when we move them to a new fileserver infrastructure. At that point we could just as easily migrate from ZFS to something else, if the something else was good enough. Btrfs currently does not qualify.)