What’s New in Apple Filesystems [pdf]

https://devstreaming-cdn.apple.com/videos/wwdc/2019/710aunvynji5emrl/710/710_whats_new_in_apple_file_systems.pdf

by sebiw • 7 years ago

198 185 7 years ago

devstreaming-cdn.apple.com

sebiw5• 7 years ago

Here's the video: https://developer.apple.com/videos/play/wwdc2019/710/

pwinnski4• 7 years ago

This is the key. The PDF fails to make sense in parts without the video.

sebiw5• 7 years ago

Initially only found the PDF, then saw the video link at the end.

DarkStar851• 7 years ago

For anyone else wondering about WWDC19, all of these PDFs are accompanied by a video. I guess they were separate in-person workshops.

msla• 7 years ago

Aren't PDFs automatically marked anymore?

sebiw5• 7 years ago

Title got renamed

kccqzy2• 7 years ago

The read-only system volume really seems like a neat idea. It reminds me of the Transactional Server role in openSUSE where they make system upgrades as atomic as possible: https://news.opensuse.org/2018/05/15/transactional-updates-i...

That said, I don't understand the use case for firm links. Seems like the problem it's trying to solve can just be solved with simple mount points: mounting read-write /Users and /usr/local. Am I missing something?

pwinnski4• 7 years ago

In the diagram, there are just two directories, and mount points could easily handle that case. In the video he describes how the scale of things makes using mount points here unwieldy.

dunham2• 7 years ago

A few more details that I've managed to suss out. The Data volume is mounted on /System/Volumes/Data. Currently, there are 21 firm links into it. They are enumerated in /usr/share/firmlinks (included below).

    /AppleInternal Device/AppleInternal
    /Applications Device/Applications
    /Library Device/Library
    /System/Library/Caches Device/System/Library/Caches
    /System/Library/Assets Device/System/Library/Assets
    /System/Library/PreinstalledAssets Device/System/Library/PreinstalledAssets
    /System/Library/AssetsV2 Device/System/Library/AssetsV2
    /System/Library/PreinstalledAssetsV2 Device/System/Library/PreinstalledAssetsV2
    /System/Library/CoreServices/CoreTypes.bundle/Contents/Library Device/System/Library/CoreServices/CoreTypes.bundle/Contents/Library
    /System/Library/Speech Device/System/Library/Speech
    /Users Users
    /Volumes Device/Volumes
    /cores Device/cores
    /home Device/home
    /mnt Device/mnt
    /opt Device/opt
    /private Device/private
    /sw Device/sw
    /usr/local Device/usr/local
    /usr/libexec/cups Device/usr/libexec/cups
    /usr/share/snmp Device/usr/share/snmp

dreamcompiler• 7 years ago

I don't understand the use case for firm links

Haven't watched the video yet, so I'm speculating. We know APFS doesn't support directory hard links, which means Time Machine can't back up to APFS. I'm guessing firm links are designed to fix this problem (perhaps among others).

dwaite5• 7 years ago

I suspect they will eventually migrate time machine backups in one go to APFS+snapshots, then use the new ASR tool also mentioned in this talk to stream local time machine snapshots to the volume.

I also suspect that will launch 'soon' (after September but possibly in March) , but I have to imagine the complexity and testing requirements for such a in-place migration are staggering.

kccqzy2• 7 years ago

With APFS supporting proper snapshots, I don't think you need directory hard links any more.

thought_alarm• 7 years ago

From the video:

"Traditionally, it was done by mounting file systems on top of directories in the root file system. With the number of crossing points which we need to introduce and the number of volumes which it would require in the file system, that approach becomes rather expensive."

h1d• 7 years ago

Why is Linux file system never really improving when there are so many potential developers? In the last 15 years I've only switched from ext3 to ext4 which isn't much of a change.

And the only alternative I hear recommended is xfs which is also around forever but not advanced, zfs is license restricted and btrfs isn't widely used enough to consider using it daily.

It's sad Linux is still stuck with basic file systems without any of the modern features to this day even though there must be huge demand for a more modern file system that can go with kernel GPL2.

Stubb2• 7 years ago

Can you back to an APFS volume yet, or does it need to be HFS+?

xemoka• 7 years ago

I was really surprised when APFS came out that it didn't support time machine. From the looks of this, it appears they're going to be able to write a new-style time machine on-top of APFS with the additions here. Interesting, over-due IMHO.

dwaite5• 7 years ago

I suspect they are waiting until they can migrate a time machine volume in one go (e.g. migrate the filesystem from HPFS with directory hard links to snapshots and a potential non-backup volume for other files).

They have a lot of deep time machine integration in other parts of the system, so I suspect the staging of the projects means it is pushed off to sometime next year.

vardump4• 7 years ago

So containers with a new bi-directional hardlink "Firmlink" (intended to be invisible to applications, link between encrypted containers), with read only volumes protecting system software.

ZFS send/receive style volume serialization for replication backup, etc. File system snapshot support included.

iOS or should I say iPadOS supports external USB media and SMB.

What seems to be missing is block level checksumming and integrity checks, scrubbing, block level duplication to protect important files, etc. No whiff of deduplication either, but that might be too memory intensive for Apple's purposes.

eclipxe• 7 years ago

iOS on iPhone also supports external USB media and SMB.

pwinnski4• 7 years ago

I was surprised to see this. From the original keynote, it seemed like an iPadOS-only option, but this video made it clear that it applies to both.

Angostura• 7 years ago

And Samba shares, which from my perspective is even more interesting.

scarface742• 7 years ago

Minor correction. Will support USB media in iOS 13.

jandrese3• 7 years ago

My understanding is that deduplication has generally been not worth the effort for a general use filesystem. The cost in memory, cpu, and sheer complexity doesn't pay off in enough storage savings. Disk space is relatively cheap. Filesystem crashes/corruption are not.

vardump4• 7 years ago

Yeah, block level deduplication is not useful for files on a typical consumer laptop. I can imagine it's even less useful for files on iOS devices.

However it is often great for virtual machines and other software development related things, as long as all the underlying block sizes and alignments match.

You really do want strong integrity guarantees though. One corrupted block can cause a lot of damage.

FPGAhacker2• 7 years ago

Disk space isn’t cheap on a Mac laptop.

Damogran6• 7 years ago

Not only that, but a Server with 100 VM's is going to have a substantial percentage of each OS image as identical...not so much on an average consumer laptop.

api• 7 years ago

Same with transparent compression in most cases.

sneak4• 7 years ago

It is a real bummer that there are still no content checksums available. One can work around this by doing sums and scrubs in userspace by storing mtime+hash in an xattr and periodically verifying and updating them. There is a utility to do this but I forgot the name.

Hackbraten• 7 years ago

I’m thinking of moving back from ZFS to APFS if I had such a workaround. Block- or file-level integrity is now the only thing that keeps me back.

zeotroph4• 7 years ago

For a company which primarily sells consumer products it makes sense to omit hardware checksums: You just detect errors which the end user might never notice, a bit flip in a picture you never look at again might not be that bad.

For anyone who has ever heard of checksums this makes APFS a no-go of course.

sneak4• 7 years ago

https://github.com/ludios/bitscrub

This is one that does it with CRC32, which may or may not be sufficient for detecting bitrot. It is probably trivial to modify to support a stronger hash.

tobias3• 7 years ago

For internal storage Apple has control over the hardware. They can just choose hardware with better internal error correction/detection, so block level checksumming on the software side doesn't make much sense in this case. For external storage it would be nice, though.

rhinoceraptor3• 7 years ago

You can't know how many uncorrectable errors you have if you're not check summing. You can't see because there are no lights. And IMO it's just negligent to believe your flash memory is 100% perfect.

theWheez• 7 years ago

Any idea how this might affect (or help) projects like iSH, or similar?

I've been fighting to be productive on my iPad, and currently that takes the form of a remote terminal.

I've been craving the ability to run a proper Unix shell locally.

lykr0n• 7 years ago

I highly doubt that you're going to get a proper shell on the iPad.

derefr• 7 years ago

I'm assuming you mean a shell into the iPad's own Unix environment. You could build something for iOS that works like Crouton does on ChromeOS just fine. (Just, nobody has done it yet, for some reason. The iPad Pro is plenty powerful enough to run VMs!)

BlackRing2• 7 years ago

Both Pythonista and OpenTerm on iOS are "good enough" for a lot of what I need, but it would be nice to have a proper shell. Even if it's jailed/locked to /private/var/mobile

larkost• 7 years ago

No effect at all. Apple is unlikely to make this possible, and given the sandboxing of Apps on iOS a meaningful version of this for local resources outside of the App are prohibited.

dlivingston• 7 years ago

Agreed. There are some basic terminals available on iOS/iPadOS though, with ssh and other capabilities, but I can't speak to how productive one could really be with them. I wholly expect to see a version of Xcode released on the iPad within the few years, though.

saagarjha6• 7 years ago

iSH is not affected, since it currently only touches files inside of its sandbox.

Wowfunhappy7• 7 years ago

Read-only state of the system volume can be disabled but not persistently, will revert to read-only after a reboot

Wait, what? Even with SIP off?

Can it be disabled from within the OS? Can I add "command-to-make-system-rw" to a launchd plist that runs at load on my machine?

nomel• 7 years ago

I think having persistent access is the file system equivalent of logging in and working entirely from root.

The default should be a restricted system, with intentional, temporary, jumps into unrestricted access for making whatever infrequent system configuration changes.

What’s the use case for constant RW access? What changes at this level so frequently?

Wowfunhappy7• 7 years ago

I think having persistent access is the file system equivalent of logging in and working entirely from root.

Except that those system files are already protected behind root privileges, so they're only read-write if I have root. And, one reason the root privilege system works is because temporarily gaining root when necessary isn't painful.

I indeed don't change root files on a daily basis, but when I do, I don't want to have to go through an extended rigamarole every single time. Typing in my password should be enough.

I totally respect that Apple wants to keep normal users out of this stuff. I just want a way to remove the safety wheels one time, instead of again and again.

BlackRing2• 7 years ago

rw file access doesn't mean there's a lack of file level permissions restricting a non sudo user from accessing an otherwise restricted file. case in point: try editing the /etc/hosts file without sudo. you can't save (without invoking sudo from within vim).

ro means no matter what I try, that file is ro unless the fs is remounted rw. Again, it doesn't negate file system level user/group permissions. and remounting a system level partition rw isn't something I'd do on a whim.

I like the idea of a ro partition for system level OS files, personally, but without user level access somehow - it's not something to be looked forward to.

mackey• 7 years ago

From the video, you can only enable read/write if you disable SIP in the first place. They didn't answer say anything about the second question.

fnord77• 7 years ago

nothing to address the docker mounted-volume slowness issue?

sigjuice• 7 years ago

It is very unlikely that docker issues are a priority for Apple.

microtherion• 7 years ago

Have you tried using delegated mounts? I got the impression these helped performance, though I have not measured details.

bni• 7 years ago

Thats probably very neat. Got rid of .DS_Store files yet?

snazz2• 7 years ago

And the .Trashes, which always manage to make my camera SD card full even after “deleting” everything. I’m not sure that there is a good solution to this other than to always use permanent deletion on removable volumes, like I think Windows does.

LeoPanthera2• 7 years ago

And the .Trashes, which always manage to make my camera SD card full even after “deleting” everything.

The trash isn't magic. You delete stuff, it goes into the Trash. The Trash is represented by a ".Trashes" directory on removable media. You can delete it manually or just empty the trash.

klodolph2• 7 years ago

This is configurable, like Thumbs.db in Windows.

bobbylarrybobby• 7 years ago

.DS_Store isn't part of the file system per se, it's part of Finder's operation.

sdan• 7 years ago

Anyone know how they made these slides? I'm speculating it's just Keynote with San Fransico Bold or something.

sebiw5• 7 years ago

According to the file's meta information, the content was created using Keynote and then converted using macOS Quartz PDF.

saagarjha6• 7 years ago

Apple's public slides are always made in Keynote using an internal template for presentations.

znep3• 7 years ago

Hopefully somehow maybe while they are in there they might do something to fix the nasty system lockups I have seen when starting both time machine and carbon copy cloner backups since switching to APFS. I'm assuming it is related to having >5 million files, but haven't figured that out for sure.

The symptoms are the system becomes almost totally unresponsive for up to 5 minutes to the point where you can't even drag and drop an existing window sometimes.

dwaite5• 7 years ago

What percentage of that do you think is Disk I/O vs lock contention?

znep3• 7 years ago

I wouldn't expect that level of disk IO to cause issues dragging existing windows around without some deeper lock contention or something, it does not behave like just IO bound. Stuff being slower, totally, but not to this level. It was never an issue before the filesystem upgrade.

sebiw5• 7 years ago

What physical medium do you use (HDD, SSD)? I had a faulty HDD act up on me like that.

znep3• 7 years ago

SSD on a 2016 macbook pro. The timing coincides exactly with the FS (and OS...) upgrade.

jhack• 7 years ago

Still nothing on transparent compression? It's one of the main reasons why I keep a ZFS partition on the Macbook.

lcnmrn• 7 years ago

There is afsctool, git clone and build from https://github.com/RJVB/afsctool or brew install afsctool (an older version).

alpb• 7 years ago

Mods: Can someone add [pdf] suffix to this please?

sctb• 7 years ago

Added. Thank you!

PaulHoule• 7 years ago

I am left with the feeling that in 2019 the filesystem is the weak part of the operating system.

* mmap doesn't really work well on 64 bit systems * mmap will block if it has to page data in from a file * there are ten different backends to handle layering on Docker and that simple fact implies that none of them are good; if you could compose layers arbitrarily the speed and scalability of Docker would be in a different league than it is now, but you can't. So Docker is just as easily something that slows you down as speeds you up. * Filesystem metadata scans are slow, shockingly so on Windows.

I know I like developing with S3-style object stores. To some extent this can replace the traditional filesystem, in other ways it can't.

mappu• 7 years ago

there are ten different backends to handle layering on Docker and that simple fact implies that none of them are good

overlay2 is fast, it's in the mainline kernel, and it's now the default for new Docker installs. I expect all the devicemapper / aufs mess to be history soon.

What’s New in Apple Filesystems [pdf]

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