(Edit: My comment is simply about the logistics and work involved in a very well executed filesystem migration. Not about whether ZFS is good for embedded or me

(Edit: My comment is simply about the logistics and work involved in a very well executed filesystem migration. Not about whether ZFS is good for embedded or memory constrained devices.) What you describe hits my ear as more NIH syndrome than technical reality. Apple’s transition to APFS was managed like you’d manage any kind of mass scale filesystem migration. I can’t imagine they’d have done anything differently if they’d have adopted ZFS. Which isn’t to say they wouldn’t have modified ZFS. But with proper driver support and testing it wouldn’t have made much difference whether they wrote their own file system or adopted an existing one. They have done a fantastic job of compartmentalizing and rationalizing their OS and user data partitions and structures. It’s not like every iPhone model has a production run that has different filesystem needs that they’d have to sort out. There was an interesting talk given at WWDC a few years ago on this. The roll out of APFS came after they’d already tested the filesystem conversion for randomized groups of devices and then eventually every single device that upgraded to one of the point releases prior to iOS 10.3. The way they did this was to basically run the conversion in memory as a logic test against real data. At the end they’d have the super block for the new APFS volume, and on a successful exit they simply discarded it instead of writing it to persistent storage. If it errored it would send a trace back to Apple. Huge amounts of testing and consistency in OS and user data partitioning and directory structures is a huge part of why that migration worked so flawlessly.