Adam Leventhal: ‘APFS in Detail’

DTrace co-creator Adam Leventhal has written a detailed analysis of APFS:

I’m not sure Apple absolutely had to replace HFS+, but likely they had passed an inflection point where continuing to maintain and evolve the 30+ year old software was more expensive than building something new. APFS is a product born of that assessment.

Based on what Apple has shown I’d surmise that its core design goals were:

  • satisfying all consumers (laptop, phone, watch, etc.)
  • encryption as a first-class citizen
  • snapshots for modernized backup.

Those are great goals that will benefit all Apple users, and based on the WWDC demos APFS seems to be on track (though the macOS Sierra beta isn’t quite as far along).

Later on:

It’s a shame that APFS lacks checksums for user data and doesn’t provide for data redundancy. Data integrity should be job one for a file system, and I believe that that’s true for a watch or phone as much as it is for a server.

I hope to see data integrity features added to APFS later, but that’s not the top priority for APFS. The top priorities for APFS are encryption/privacy, and energy efficiency. Redundancy and checksums make perfect sense for a machine plugged into the wall; they create a trade-off for devices that run on batteries. I think we’ll see these features eventually in APFS, but I’m not surprised they didn’t make the first cut.

See also: “Introducing Apple File System”, Session 701 at WWDC 2016.

Monday, 20 June 2016