They cant ship it for licensing reasons. Which means they cant support it either.
It's what happens when ideology is allowed to trump technology, and it is sad.
The fact that various distros ship not-open video card drivers shows that for some things, there's a willingness to compromise. This is far "worse" than shipping an open source module, or open source code that is compiled into a module on install, either of which could be done for ZFS.
Linux and ZFS's licenses are incompatible, which would make it illegal to distribute them together. Both ZFS and Linux copyright owners could choose to sue any entity that would distribute Linux with ZFS support.
As I said to the other poster, you're just spreading FUD.
Licenses allow you to distribute things despite copyright. Usually distributing software without a license is illegal, though there are exceptions in some countries for music and movies.
You can obviously nitpick about that he uses "illegal". However, the discussion was about why ZFS is not distributed. That is what the answer was about, incompatible licenses making it (somewhat) impossible for distributions to carry it.
Now various distributions do have e.g. "nonfree" repositories, but incompatible licenses are a big problem. Responding to such concerns with "just spreading FUD" seems to (hopefully) indicate you're not involved with any distribution.
http://phoronix.com/forums/showthread.php?79312-ZFS-On-Linux...
Try to be concrete, just "FUD FUD FUD" is not impressive as an answer.
The GPL gives you a license to distribute IF AND ONLY IF all the linked binaries have AT LEAST the same permissive rights as the GPL mandates. The CDDL gives rights SIMILAR to GPL, but in a way that is incompatible, i.e. which does not let you distribute CDDL code with all the permissions the GPL mandates. As such, you void the license to distribute the GPL code, as you're unable to comply with the GPL license (i.e. the bit that all linked binaries have at least the GPL enforced liberties).
The GPL's license to distribute is dependent on you distributing binaries with the appropriate permissions and the CDDL won't let you.
Richard Yao from Gentoo summarizes it quite well (http://phoronix.com/forums/showthread.php?79312-ZFS-On-Linux...).
I don't think lack of manpower has been the only thing preventing it. I think idealogical issues are the main factor.
ZFS could be shipped in a similar manner to drivers, by requiring explicit user action to enable (I believe this is what Gentoo are doing). However, it makes a lot less sense for a filesystem, since the switching costs are much higher than for a graphics driver.
It would at least breach ZFS's license to ship it.
In the case of Linux, the author has expressed an explicit opinion that most linux+driver combination do not create a derivative work.
The GPL puts no restrictions on use, i.e. once you've got both linux and your non-open drivers the GPL doesn't care whether you combine the two.
Additionally, as people point out the license can only be enforced by copyright holders, so if no linux copyright owners bother to sue people distributing non-open drivers, nothing will happen.
This is however rather shaky legal ground, as at any point you could get sued for violating the license. This also why linux doesn't ship ZFS, since the CDDL is incompatible with GPL any company distributing linux with ZFS would open itself to a potential lawsuit by any linux copyright holder. You can imagine most companies are not very happy taking this risk.
With regards to Richard Yao's comments, of course he's not worried. Copyright violation (which is what breaking the GPL is) only lets you sue for monetary damages or to stop the distribution. There's zero reason for people to sue most linux distros as they're non-profits that aren't charging for distribution. Since it's nearly impossible to show monetary loss by a linux copyright holder (it's being distributed for free!) The only thing to possibly do would be to sue the distros into ceasing distribution, which seems an undesirable outcome for most linux copyright holders, so that's unlikely to be enforced.
Since GPL doesn't restrict actual usage the users of these distros have nothing to worry about anyway.
In summary, you only have to worry about being sued if you are both violating the GPL and making some sort of money while doing it. But the fact that you probably won't get sued doesn't mean that what you are doing is not illegal.
- Well, in any country that's signed the Berne Convention, anyway.
If you really think you can do something illegal because just you're able to do that, oops…!
Please provide reasoning why you think it's "illegal." Otherwise, you're just spreading FUD, which is the whole reason for people believing a Linux distribution can't ship ZFS on Linux in the first place.
http://zfsonlinux.org/faq.html#WhatAboutTheLicensingIssue makes some funny claims about "same binary". GPL is not about "same binary" at all.