| What a great and valuable post, especially since this info is the result of talking to the APFS team at WWDC, and has not been published anywhere else yet. Of particular interest (to me) was the "Checksums" section: Notably absent from the APFS intro talk was any mention of
checksums....APFS checksums its own metadata but not user data.
...The APFS engineers I talked to cited strong ECC protection
within Apple storage devices. Both flash SSDs and magnetic media
HDDs use redundant data to detect and correct errors. The
engineers contend that Apple devices basically don’t return
bogus data.
That is utterly disappointing. SSDs have internal checksums, sure, but there are so many different ways and different points at which a bit can be flipped.It's hard for me to imagine a worse starting point to conceive a new filesystem than "let's assume our data storage devices are perfect, and never have any faulty components or firmware bugs". ZFS has a lot of features, but data integrity is the feature. I get that maybe a checksumming filesystem could conceivably be too computationally expensive for the little jewelry-computers Apple is into these days, but it's a terrible omission on something that is supposed to be the new filesystem for macOS. |
Their filesystem goals are in some ways consistent with Apple's (marketing) vision: Users would never have terabyte libraries of anything, as the various iServices would (should) be hosting that stuff in the cloud (where one presumes it is stored on a filesystem that actually includes data integrity). Since users won't be storing much of anything locally, Apple needn't care too much about data integrity. This is of course, nonsense.
The idea that Apple's storage devices are error-free is arrogant--but even assuming that were true, there can still be bit errors in the SATA/PCI bus, errors in memory, race conditions, gamma rays, etc. Apple uses ECC memory on their Mac Pro, so obviously someone still believes that sort of thing is possible.