“For Mac geeks of a certain persuasion, the first mention of a soon-to-be-revealed feature of Leopard during the WWDC keynote set off a mental chain-reaction,” John Siracusa writes for Ars Technica. “That feature was Time Machine, and the name alone was enough to cause one particular phrase to hammer in the mind of many people, including me: ‘New file system in Leopard!‘”
Siracusa asks, “Why should the mere name ‘Time Machine’ scream “new file system” to anyone? And why the excitement about a new file system in the first place? What’s wrong with HFS+, Mac OS X’s current file system? It’s got journaling. It supports arbitrarily extensible metadata. It can even be case-sensitive to satisfy the Unix geeks. Does Mac OS X really need a new file system?”
Siracusa writes, “In a word, yes. HFS was a state-of-the-art personal computer file system when it was first released…twenty-one years ago. HFS+ is only eight years old, but it’s built on many of the design decisions of HFS. Progress marches on. Today, there are new capabilities that the best modern file systems have, but that HFS+, even with all of its recent additions, does not. Here’s a short list.”
• Efficient storage and handling of very small files.
• Logical volume management through a pooled storage model.
• Improved data integrity using checksums on all data.
• Snapshots.
“It’s no surprise that many of those bullet points were pulled from the ZFS home page,” Siracusa writes. “File system nerd knows that snapshots are not the kind of feature that’s easy to tack onto an existing file system. HFS+ has already been extended significantly past its original abilities. Trying to add snapshots is probably one extension too far. So snapshots probably mean a new file system.”
“As the Time Machine demonstration progressed, revealing the user interface’s Core Animation flourishes, nothing shown precluded the existence of a new file system with support for snapshots. On the other hand, nothing about a new file system was mentioned explicitly either. You’d think this would be the type of thing that Apple would want to tout. If Time Machine isn’t powered by a new, snapshot-enabled file system from Apple, then how does it work? It’s got to be snapshots, right? File system nerds began to worry,” Siracusa writes. “Wait! Maybe Apple didn’t say anything about a new file system because the one they’re using was created by someone else. Maybe Apple is moving to ZFS in Leopard!”
Or maybe not. Siracusa later explains, “Time Machine is not an interface to file system snapshots built on any sort of new, modern file system. Instead, it’s an automated backup system that works with plain old HFS+… Does Time Machine suck because it doesn’t use snapshots? No… As for the future of file systems in Mac OS X, I continue to hold out hope that something more modern will replace HFS+… Although I would be satisfied with ZFS, I think Apple has a unique perspective on computing that might lead to a home-grown file system with some interesting attributes.”
Full article, with much, much more, here.