APFS in Detail
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.