Apple now says that the ZFS file system will be available in the forthcoming Mac operating system, sort of.

Seeking to clarify a statement made on Monday by Brian Croll, senior director of Mac OS X Product Marketing, to two InformationWeek reporters that Apple's new "Leopard" operating system would not include the ZFS file system, an Apple spokesperson indicated that ZFS would be available as a limited option, but not as the default file system.

ZFS "is only available a read-only option from the command line," according to an Apple spokesperson.

In a follow-up interview today, Croll explained, "ZFS is not the default file system for Leopard. We are exploring it as a file system option for high-end storage systems with really large storage. As a result, we have included ZFS -- a read-only copy of ZFS -- in Leopard."

"Read-only means that at a later date, if there are ZFS volumes, those systems would be able to read ZFS volumes," Croll added. "You cannot write data into the system. It will allow you to read ZFS volumes later."

Asked whether ZFS might be implemented for Apple's Xserve rack mountable server line, Croll said, "Where we head in the future, we're not able to talk about."

ZFS is a 128-bit open-source file system originally created for Sun's Solaris operating system. It is widely seen as a more robust alternative to Apple's current HFS+ file system.

InformationWeek requested a preview copy of "Leopard," but Apple representatives declined to provide one. Several developers at Apple's Worldwide Developer Conference who were approached for comment about Leopard declined to speak, citing non-disclosure agreements with Apple.

According to one InformationWeek reader posting to our forum under the name "Akie," ZFS can be accessed through the Disk Utility program, under the Erase menu. "Sun hasn't got Solaris to run with ZFS as the boot drive, or at least reliably, so ZFS is only available on non-boot drives on Sun systems, so this is also the case for Leopard," said Akie, adding that Leopard includes a new form of RAID called RAID-Z, "which uses ZFS and overcomes one of the major problems with RAID, the write hole."

The "write hole" is a problem with the RAID-5 implementation that permits data loss following a loss of power or crash.