Can I trust that ZFS is consistent between Linux and FreeBSD?

I'm planning to build a FreeNAS box sometime soon, but if ZFS on Linux eventually proves to be reliable, I might want to switch, just to have a more familiar OS.

So I'm wondering if I can trust that the different implementations of ZFS are compatible. In other words, if I just swap out the boot disk from FreeNAS to Linux or OpenIndiana, can I trust that nothing bad will happen to my data?

This may seem like a stupid question--obviously it ought to be compatible--but I'm guessing that ZFS isn't commonly used in cases where drives are moved between computers, so I'm hoping someone can provide a better answer than just "it ought to be".

You should pay close attention to the zpool versions. That's the major differentiator between the Oracle, former-OpenSolaris, Linux and *BSD variants of ZFS.

Basically, you can upgrade an older zpool to a newer version, but you cannot downgrade.

Oddly-enough, Wikipedia has the best summary of the different zpool versions and the differences between them.

The current list of zpool versions amongst ZFS implementations is here.

I use NexentaStor 3.1. According to that schedule, I'd be able to work with ZFS filesystems from OpenIndiana and FreeBSD, but NOT Solaris 11, for example.

I do believe FreeNAS is on a super-old version of ZFS, though. Consider Nexenta?

The future of ZFS development outside of Oracle will introduce ZFS Feature Flags. This should make it possible for you to use a newer ZFS system on a storage pool based on an older ZFS version. So the answer is yes, it should be safe to start with FreeNAS today and move to Linux later when ZFS there is more mature.

I know FreeBSD now follows the ZFS changes in Illumos very closely. New bugfixes or features are added to FreeBSD-HEAD in matter of days or weeks. I also believe the zfsonlinux project follows ZFS changes in the Illumos ZFS source. And they most likely will have ZFS Feature Flags, if it's not already added. But they do at the moment have a higher priority reaching the stability and quality level that Illumos and FreeBSD has.