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APFS in Detail

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Re: APFS in Detail

#2

Post by idorosen »

In my opinion, APFS does not seem to improve upon ZFS in several key areas (compression, sending/receiving snapshots, dedup, etc.). Apple is reimplementing many features already implemented in OpenZFS, btrfs (which itself reimplemented a lot of ZFS features), BSD HAMMER, etc.

Maybe extending one of these existing filesystems to add any functionality Apple needs on top of its existing features (and, hopefully, contributing that back to the open source implementation) would cost more person-hours than implementing APFS from scratch. Maybe not.

Either way, we will now have yet another filesystem to contend with, implement in non-Darwin kernels (maybe), and this adds to the overall support overhead of all operating systems that want to be compatible with Apple devices. Since the older versions of macOS (OSX) don't support APFS, only HFS+, this means Apple and others will also have to continue supporting HFS+. It just seems wasteful of everyone's time to me.

Also: https://xkcd.com/927/

Re: APFS in Detail

#3

Post by niftich »

The file-level deduplication [1] is interesting. Not being a filesystem expert, this sounds like it fulfills a similar usecase to snapshots [2]. Or am I reading this wrong?

Is NTFS's shadow copy like Snapshots?

[1] http://dtrace.org/blogs/ahl/2016/06/19/apfs-part3/#apfs-clon...

[2] http://dtrace.org/blogs/ahl/2016/06/19/apfs-part2/#apfs-snap...

Re: APFS in Detail

#4

Post by lanna »

idorosen wrote: post #2

In my opinion, APFS does not seem to improve upon ZFS in several key areas (compression, sending/receiving snapshots, dedup, etc.). Apple is reimplementing many features already implemented in OpenZFS, btrfs (which itself reimplemented a lot of ZFS features), BSD HAMMER, etc. Maybe extending one of these existing filesystems to add any functionality Apple needs on top of its existing features (and, hopefully, contrib…

Breaking changes sometimes are unavoidable, progress has to be made.

Re: APFS in Detail

#5

Post by matthewmcg »

idorosen wrote: post #2

In my opinion, APFS does not seem to improve upon ZFS in several key areas (compression, sending/receiving snapshots, dedup, etc.). Apple is reimplementing many features already implemented in OpenZFS, btrfs (which itself reimplemented a lot of ZFS features), BSD HAMMER, etc. Maybe extending one of these existing filesystems to add any functionality Apple needs on top of its existing features (and, hopefully, contrib…

Agreed. A few years ago Apple was on the verge of using ZFS but cancelled the project due to licensing issues.

See http://arstechnica.com/apple/2009/10/apple-abandons-zfs-on-m...

Re: APFS in Detail

#6

Post by TazeTSchnitzel »

> Also, APFS removes the most common way of a user achieving local data redundancy: copying files. A copied file in APFS actually creates a lightweight clone with no duplicated data.

No, it doesn't. APFS supports copying files, if you want that. It's just that the default in Finder is to make a “clone” (copy-on-write).

Re: APFS in Detail

#7

Post by veidr »

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.

Re: APFS in Detail

#8

Post by rincebrain »

niftich wrote: post #3

The file-level deduplication [1] is interesting. Not being a filesystem expert, this sounds like it fulfills a similar usecase to snapshots [2]. Or am I reading this wrong? Is NTFS's shadow copy like Snapshots? [1] http://dtrace.org/blogs/ahl/2016/06/19/apfs-part3/#apfs-clon... [2] http://dtrace.org/blogs/ahl/2016/06/19/apfs-part2/#apfs-snap...

NTFS Shadow Copies are more like LVM/ZFS snapshots than APFS's file-level CoW snapshots, in that they both operate on the entire volume at block-level, rather than having a per-file level of granularity.

There are other FSes that allow the behavior that APFS is demonstrating - look at OCFS2 and Btrfs, both of which allow you to do cp --reflink.

Re: APFS in Detail

#9

Post by mindajar »

idorosen wrote: post #2

In my opinion, APFS does not seem to improve upon ZFS in several key areas (compression, sending/receiving snapshots, dedup, etc.). Apple is reimplementing many features already implemented in OpenZFS, btrfs (which itself reimplemented a lot of ZFS features), BSD HAMMER, etc. Maybe extending one of these existing filesystems to add any functionality Apple needs on top of its existing features (and, hopefully, contrib…

Classic comic, but I don't think it applies. APFS looks intended to solve Apple's product problems really well, and it doesn't even try to be a filesystem for everyone.

Apple has said from time to time that they're all about owning and controlling the key technologies that go into their products. APFS makes a lot of sense from that perspective, and this seems one of those cases where going their own way is better than importing someone else's constraints. ZFS on an Apple Watch? LOL.

Re: APFS in Detail

#10

Post by scarface74 »

idorosen wrote: post #2

In my opinion, APFS does not seem to improve upon ZFS in several key areas (compression, sending/receiving snapshots, dedup, etc.). Apple is reimplementing many features already implemented in OpenZFS, btrfs (which itself reimplemented a lot of ZFS features), BSD HAMMER, etc. Maybe extending one of these existing filesystems to add any functionality Apple needs on top of its existing features (and, hopefully, contrib…

Is ZFS lightweight enough to run on the watch? Their ultimate goal was to have a file system efficient enough and flexible enough to run across all of their OS's - MacOS, iOS, tvOs, and watchOS
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