Will HFS+ extended attributes be lost on FreeNAS?
FreeNAS supports the creation of AFP file shares for general use with OS X systems. For Time Machine backups, you need to make sure to specifically enable Time Machine support (Disk Discovery enabled and type set to Time Machine) on a particular AFP share you intend to use.

Further clarification:  AFP currently supports Unicode file names, POSIX and access control list permissions, resource forks, named extended attributes, and advanced file locking.

From http://en.wikipedia.org/wiki/Apple_Filing_Protocol