Apple and ZFS

What is going on with Apple and Sun’s ZFS (Zettabyte File System)?

ZFS, based at least in part on NetApp’s WAFL (Write Anywhere File Layout), has a 128-bit addressing scheme and can address 256 quadrillion zettabytes. A zettabyte is 1 billion terabytes. The basic capacity is just huge. ZFS delivers one storage volume to a host computer’s O/S and abstracts all the component disk drives and arrays to form that volume. Sun says that it has profound administration and data security advantages over other file systems.

When asked about its use by Apple, the company’s server and storage product manager, Doug Brooks, said this: “There are lots of file systems. HMS+ is the default Mac OS file system and it has a 16TB limit with its 4-byte block size. Xsan has a 2PB limit because it has a much larger block size. A feature added to Leopard Server is a customisable block size. By doubling it to 8 you get a 32TB limit.”

“Storage needs are constantly growing. We’ll hit the 6TB limit. There are already 1TB drives. Maybe 2TB, even 4TB ones are coming. So ZFS is a technology preview in Leopard. A ZFS volume in Leopard today will mount. We want developers to try it out and let us know what they think.”

“ZFS is a very interesting file system with storage pools and capacity placement. It has a long way to go. For example, it’s not bootable; you can’t boot a Mac off it. It’s implemented in user space and not kernel space which is radically different. It’s not optimised for the way the Mac works.”

“We’re working on it. Maybe in the future, if it becomes the file system of choice, we’ll implement it. Most file systems take years and years of development. File systems are definitely not things that occur overnight.”

Sun has a lawsuit pending with NetApp which claims it has infringed its patents. Apple may be concerned on that score although Sun has said it will indemnify ZFS users.

Apple’s use of technology inclines us to think that it wants to construct semi-walled gardens for its users, such as Xsan, and is not interested in using any technology that would commoditise Macs, either servers or clients.

As with other technology choices Apple will think long and hard about whether to use ZFS and, inevitably, goes its own individual way if it does so. As with Blu-ray Apple loves to keep us guessing.

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