Complex sentence: FreeBSD added read-only support for XFS in December 2005 and in June 2006 introduced experimental write support; however this was intended only as an aid in migration from Linux, not as a "main" file system.
Split into simpler sentences: FreeBSD added read-only support for XFS in December 2005, and in June 2006 introduced experimental write support. However, this was intended only as an aid in migration from Linux, not as a "main" file system.