I shared an office with Noel Dellofano when she was porting ZFS over to the Mac. It was definitely an uphill battle but she got through it small piece by piece,

I shared an office with Noel Dellofano when she was porting ZFS over to the Mac. It was definitely an uphill battle but she got through it small piece by piece, with patience. I originally was hoping to get the project, but in retrospect she was much better at it than I ever could have been. As far as I remember, there was too much licensing uncertainty around it for it to be give the green flag. That said, from my ancient memory, it began as a side project for Don Brady (one of the core file system team members). So it may have fared better if it had top down support from the beginning.