FreeBSD has been shipping with integrated support for the ZFS advanced file system for several years. The implementation of ZFS the FreeBSD operating system uses is imported from the Illumos project and lightly modified to make it work on FreeBSD. Other ports of ZFS traditionally came from the Illumos implementation too. However, the focus of development has shifted and now the bulk of work being done on ZFS is being done through the ZFS on Linux (ZoL) project. This has lead some FreeBSD developers to decide to rebase FreeBSD's ZFS implementation off the Linux port. Matthew Macy explains: "FreeBSD has regularly pulled changes from Illumos and tried to push back any bug fixes and new features done in the context of FreeBSD. In the past few years the vast majority of new development in ZFS has taken place in DelphixOS and ZFS on Linux (ZoL). Earlier this year Delphix announced that they will be moving to ZoL. This shift means that there will be little to no net new development of Illumos. While working through the git history of ZoL I have also discovered that many races and locking bugs have been fixed in ZoL and never made it back to Illumos and thus FreeBSD. This state of affairs has led to a general agreement among the stakeholders that I have spoken to that it makes sense to rebase FreeBSD's ZFS on ZoL. Brian Behlendorf has graciously encouraged me to add FreeBSD support directly to ZoL so that we might all have a single shared code base."