[inkyoto]

Supporting ZFS in a UNIX kernel requires excessively extensive modifications to the design and implementation of the VMM, namely:

  1. Integration of the kernel's VM with ZFS's adaptive replacement cache which runs in user space – memory pressure cooperation, page accounting and unified memory management. It also requires extensive VM modifications to support ZFS's controlled page eviction, fine-grained dirty page tracking, plus other stuff.

  2. VMM alignment with the ZFS transactional semantics and intent logs – delayed write optimisations, efficient page syncing.

  3. Support for large memory pages and proper memory page alignment – support for superpages (to reduce the TLB pressure and to efficiently map large ZFS blocks efficiently) and I/O alignment awareness (to ensure proper alignment of memory pages to avoid unnecessary copies).

  4. Memory-mapped I/O: different implementation of mmap and support for lazy checksumming for mmap pages.

  5. Integration with kernel thread management and scheduling, co-opertation with VMM memmory allocators.

  6. … and the list goes on and on.

ZFS is just not the right answer for consumer facing and mobile/portable devices due being a heavyweight server design with vastly different design provisions and due to being the answer to a entirely different question.

[AndrewDavis]

> Supporting ZFS in a UNIX kernel requires excessively extensive modifications to the design and implementation of the VMM, namely:

FYI: Apple did a bunch of that work. They ported ZFS to OSX shortly after it was open sourced. With with only support landing in 10.5. With it being listed as an upcoming feature in 10.6.

But something happened and they abandoned it. The rumour is a sun exec let the cat out of the bag about it being the next main filesystem for osx (ie not just support for non root drives) and this annoyed Jobs so much he canned the whole project.

[flomo]

> But something happened and they abandoned it. The rumour is...

The reality is NetApp sued Sun/Oracle over ZFS patents.

https://www.theregister.com/2010/09/09/oracle_netapp_zfs_dis...

[inkyoto]

Yes, they did, but… it was more of a proof of concept and a promise rather than a production quality release. They also had the OS X Server product line at the time (no more), which ZFS would have been the best fit for at the time, and they also released the OS X ZFS port before the advent of the first iPhone.

It is not a given that ZFS would have performed well within the tight hardware constraints of the first ten or so generations of the iPhone – file systems such as APFS, btrfs or bcachefs are better suited for the needs of mobile platforms.

Another conundrum with ZFS is that ZFS disk pools really, really want a RAID setup, which is not a consumer grade thing, and Apple is a consumer company. Even if ZFS did see the light back then, there is no guarantee it would have lived on – I am not sure, anyway.

[lunarlull]

> The rumour is a sun exec let the cat out of the bag about it being the next main filesystem for osx (ie not just support for non root drives) and this annoyed Jobs so much he canned the whole project.

Very petty if true.

[MBCook]

It would fit jobs though.

That’s one of the famous rumors.

As others here have said Oracle bought Sun two years later. Between me increased memory requirements, uncertainty due to Sun’s status as an ongoing concern, and who knows what else maybe it really did make sense not to go forward.

[kergonath]

As other also said, there were patent issues around ZFS: https://wiki.endsoftwarepatents.org/wiki/NetApp's_filesystem...

[JCattheATM]

The ZFS code was already released under the CDDL. What was stopping Apple from writing their own implementation like OpenZFS and FreeBSD, regardless of what happened with Sun?