I've been trying out ZfsOnLinux, which seems pretty stable according to a couple of friends.
In addition to the usual stuff, I had to make two symlinks to get DKMS to work on CentOS 6.4.
First, the post-install script DKMS uses is pointed to /usr/lib/ and not /usr/lib64/ (this should probably get fixed some other way):
ln -s /usr/lib64/dkms /usr/lib/dkms
Also, the kernel build is using the fully-qualified version and not the abbreviated one:
ln -s /usr/src/kernels/2.6.32-358.14.1.el6.x86_64 /usr/src/kernels/2.6.32-358.el6.x86_64
There is probably some reason for all this, or it will be fixed in a week. But anyway, it might save you time this week. It compiles the kernel module for me now.