ZFS: Apple's new filesystem that wasn't (2016)

Since Apple was already integrating custom SSD controllers onto their A series SOCs, presumably the purchase was about Anobit patents.

> Anobit appears to be applying a lot of signal processing techniques in addition to ECC to address the issue of NAND reliability and data retention... promising significant improvements in NAND longevity and reliability. At the high end Anobit promises 50,000 p/e cycles out of consumer grade MLC NAND

https://www.anandtech.com/show/5258/apple-acquires-anobit-br...

Apple has said in the past that they are addressing improved data stability at the hardware level, presumably using those acquired patents.

> Explicitly not checksumming user data is a little more interesting. The APFS engineers I talked to cited strong ECC protection within Apple storage devices... The devices have a bit error rate that's low enough to expect no errors over the device's lifetime.

https://arstechnica.com/gadgets/2016/06/a-zfs-developers-ana...

But I agree with you about the most important feature that Apple failed on.

I lament Apple's failure to secure ZFS as much as the next Mac user, but I understood that ship to have sailed when it did, around a decade ago.

But as a desktop user, I almost threw up in my mouth when APFS came out with no checksums for user data. I'd assumed if they were going to pass on ZFS they would reimplement the most critical feature. But they didn't. I know I've lost data because of it, and if you have a few TB of data, I suspect you have, too.

Not lost permanently, because I had manually-checksummed backups. But lost in the sense that the copies of the data made on macOS were corrupted and different, and the OS/filesystem simply didn't notice. Oops!

Once you've used ZFS, that's unforgivable. I mean, ZFS has had some bugs, over the years (well mainly just last year lol), and a small number of users have lost data due to that. But to silently lose data by design? Fuck all the way off. It's 2025, not 1985.

So while APFS has some cool modern features (or at least two), it's an embarassment. (And all my non-ephemeral storage is now on Linux.)

> HFS improved upon the Macintosh File System by adding—wait for it—hierarchy! No longer would files accumulate in a single pile; you could organize them in folders.

MFS did allow you to organize your files into folders, but on-disk they were represented as a single list of files with unique filenames - meaning you could have 'resume.txt' in a folder called 'Jan's Docs' but you couldn't also have 'resume.txt' in a folder called 'Jake's Docs' - every file on the disk needed to have a unique filename.

Not so much an issue in the days of 400KB floppy drives, but once people started getting 20 MB hard drives that was going to be an unacceptable limitation.

The other major benefit of HFS was that it stored file data in a B-tree, which allowed directory information to be stored effectively hierarchically, meaning you could find a directory's contents very quickly. With MFS, every file being stored in a single list meant that any time you wanted to get a directory's contents you had to read through that list of every file on the disk to see which ones were stored in that directory, so every listing of any directory was O(n) for the total number of files on the disk.

I imagine the situation would have been different if Apple's ZFS integration had completed and shipped before Sun's demise.

They didn't rip out DTrace, after all.

We don't know exactly what happened with Apple and Sun, but there were lots of indicia that Apple wanted indemnification and Sun was unwilling to go there. Why Apple really insisted on that, I don't know -- I think they should have been able to do the prior art search and know that NetApp probably wouldn't win their lawsuits, but hey, lawsuits are a somewhat random function and I guess Apple didn't want NetApp holding them by the short ones. DTrace they could remove, but removing ZFS once they were reliant on it would be much much harder.