Expected to arrive several years ago in Mac OS X 10.5 "Leopard," Sun's ZFS file system was early in the year announced for release in Snow Leopard Server. However, Apple this week pulled the plug on the port.
According to reports, the primary cause was failure to reach licensing terms with Sun, which is now owned by Oracle. The Mac OS SourceForge page says that the project has been discontinued and that its listserv and code repository will be taken down shortly.
Here's a bit of the Ars Technica post on the project's end:
Apple then launched an open source project to port ZFS, and it was expected that Apple would include full support in Snow Leopard. Once details of the operating system were announced, though, it was revealed that only Snow Leopard Server would have ZFS support. But all mention of ZFS support was wiped from the Snow Leopard server pages on Apple's website shortly before Mac OS X 10.6 launched, and the feature was pulled from the final shipping version.
John Gruber at Daring Fireball wondered if concerns about NetApp's patent filing over ZFS might have done it in.
Here's my two cents: All of the above helped Apple managers to pull the trigger. But my bet is that after years of effort, there wasn't an end in sight for getting ZFS to work on the majority (or even sizable minorty) of the machines that Apple makes.
ZFS was designed for servers and big iron and the task of getting it to work efficiently in a client and future microclient architectures wasn't going to work. Likely there were issues with getting it to play nicely with legacy devices.
With all the unknowns hanging over ZFS adoption, Apple decided it will be better in the long run, and maybe even in the short run, to write something new.