Check out this post from the FreeBSD Foundation, regarding ZFS. There is also a lengthy discussion on ycombinator regarding the licensing issues surrounding the filesystem.
ZFS has been making headlines lately, so it seems like the right time to talk about the longstanding relationship between FreeBSD and ZFS.
For nearly seven years, FreeBSD has included a production quality ZFS implementation, making it one of the key features of the FreeBSD operating system. ZFS is a combined file system and volume manager. Decoupling physical media from logical volumes allows free space to be efficiently shared between all of the file systems. ZFS introduced unprecedented data integrity and reliability guarantees to storage on FreeBSD. ZFS supports varying levels of redundancy for tolerance of hardware failures and includes cryptographic checksums on all data to guard against corruption.
FreeBSD Foundation – FreeBSD and ZFS: http://freebsdfoundation.blogspot.com/2016/02/freebsd-and-zfs.html
Discussion on ycombinator: https://news.ycombinator.com/item?id=11185581