[HN Gopher] macOS Tahoe brings a new disk image format
___________________________________________________________________
macOS Tahoe brings a new disk image format
Author : zdw
Score : 306 points
Date : 2025-06-12 15:49 UTC (7 hours ago)
(HTM) web link (eclecticlight.co)
(TXT) w3m dump (eclecticlight.co)
| bigyabai wrote:
| My kingdom for a documented disk image format.
| aaronmdjones wrote:
| https://docs.kernel.org/filesystems/ext4/index.html
| zymhan wrote:
| A filesystem is not a disk image.
| n_plus_1_acc wrote:
| If it quaks like a disk image, it is a disk image
| duskwuff wrote:
| A filesystem is not a file.
|
| (Yes, you can store a filesystem in a file - and that's a
| trivial sort of disk image, but one with some serious
| drawbacks like "you have to allocate all of the space up
| front". We can do better.)
| zymhan wrote:
| What?
| shakna wrote:
| About the only decently documented disk image format I've found
| is qcow2. [0] Which is usually not the best tool for the job.
|
| So very many of them are just header details + "only works with
| our tools".
|
| [0] https://www.qemu.org/docs/master/interop/qcow2.html
| mannyv wrote:
| I'll take your kingdom!
|
| ISO 9660.
|
| https://www.iso.org/iso-9660-images-for-computer-files.html
|
| VMDK
|
| https://en.wikipedia.org/wiki/VMDK
|
| Amiga
|
| https://en.wikipedia.org/wiki/Amiga_Disk_File
|
| UDF
|
| https://en.wikipedia.org/wiki/Universal_Disk_Format
|
| Apple Disk Image
|
| https://en.wikipedia.org/wiki/Apple_Disk_Image
| shakna wrote:
| VMDK isn't documented there, and is a container for multiple
| partially documented - and some only reverse engineered -
| subformats.
| mdaniel wrote:
| Not on wikipedia, but VMDK is part of the DTMF OVF[1]
| format and thus I believe the .vmdk format would be
| implicitly made available therein
|
| However, words are words but software is better:
|
| - https://github.com/vmware/open-vmdk#specifications is
| Apache 2
|
| - the link they cited is bitrotten but Internet Archive has
| you: https://web.archive.org/web/20210411181842/https://www
| .vmwar...
|
| 1: https://www.dmtf.org/standards/ovf
| bowsamic wrote:
| My favourite blog specifically for the painting articles
| baggy_trough wrote:
| They are amazing, for sure.
| chrisweekly wrote:
| Yes! So glad GP brought that up. Bookmarked, looking fwd to
| spending more time absorbing the fantastic images and
| accompanying texts.
| lucasoshiro wrote:
| Nice. But I would like it better if the effort was to support
| ext4, BtrFS, NTFS and other popular filesystems from the Linux
| and Windows world...
| gjsman-1000 wrote:
| ext4 and Btrfs are only well supported on Linux; they are not
| universal standards.
|
| NTFS was only supported well on Windows until recently; but
| extensions like NTFS Encryption (BitLocker) are still Windows
| only. Mac still does not let you write to an NTFS volume.
|
| APFS and HFS+ are obviously Apple file systems.
|
| FreeBSD does not support ext4 or Btrfs well; but instead
| prefers UFS2 or ZFS despite also being an open-source Unix-
| inspired OS.
|
| The world runs on proprietary or non-universal file systems
| with CDFS (ISO 9660), FAT, and exFAT being the sole exceptions.
| nemomarx wrote:
| if Mac also supported Linux file formats they would get
| closer to universal, though? we can't get to that world
| without these individual steps.
|
| creating a new non universal one is backing away from it
| gjsman-1000 wrote:
| Even FreeBSD can't be bothered to do a good job supporting
| Linux file systems. They're basically proprietary siloed
| file systems like the rest, even if code is available.
| Linux, meanwhile, can't be bothered to support _either_ of
| FreeBSD 's file systems officially. UFS2 is hardly patented
| anymore, but Linux doesn't care beyond read-only support.
|
| Being open-source, and even being in a popular open-source
| project, does not make a standard, or even imply
| inferiority to those who do not implement it.
|
| https://xkcd.com/927/
| bombcar wrote:
| There might be some license issues, but the dirty secret
| is filesystem portability isn't terribly important, and
| for the users for whom it is - ExFAT and friends are
| usually good enough.
| johnfernow wrote:
| exFAT is widely used but it not being journaled has led
| to so many thousands (if not more) people losing tons of
| data, many of which wouldn't have lost so much data had
| they used a journaled filesystem (or even one with
| redundant file tables.)
|
| If you need to connect a portable drive to machines of
| different OS's, there is no safe filesystem that supports
| read and write on both Windows and MacOS.
|
| Alternatively, cloud storage works until the files are
| larger than the space you have left on
| Drive/Dropbox/OneDrive/etc., and local network sharing
| (on certain networks at least) is more complicated than
| what the average user is willing to put up with. In
| practice, many use USB flash drives or external HDDs/SSDs
| with exFAT. Yeah, people should have more than one
| backup, but we know in the real world that's not what
| many do. That requires them spending more time (e.g.
| configuring local network sharing or setting up an old
| machine lying around to be a NAS) or money (more on cloud
| storage.) In practice, having a cross-platform, journaled
| filesystem would lead to a lot less data loss.
|
| Aside from exFAT, the only alternative with native cross-
| platform R/W capability is FAT32, but while it has a
| redundant file allocation table (unlike exFAT), it has a
| max file size of 4GB, which limits its usefulness for
| many workflows.
| atonse wrote:
| Does this even matter, if you can copy/mount files over a
| network?
|
| What are potential use cases where you'd want to support
| those additional file systems? External drives?
| cortesoft wrote:
| I just ran into a use case yesterday. I wanted to copy
| some files from either my Mac or my Windows machine onto
| the MicroSD card for my SteamDeck, which is ext4.
|
| I wanted to just plug in the card and copy files, but
| couldn't.
| atonse wrote:
| Interesting, ok.
|
| I don't even want to say "Use NTFS, doesn't everything
| support it?" because I'm not even sure that's the best
| solution for an SD card.
|
| Maybe with their new FSKit API [1], someone can build a
| compatibility layer for it.
|
| 1: https://developer.apple.com/documentation/fskit?langua
| ge=obj...
| bombcar wrote:
| Is there a single filesystem in the world (besides "simple"
| ones like FAT) that both has an open standard AND is licensed
| in a "usable" codebase (MIT or other "non-copyleft" license)?
| dataflow wrote:
| I think UDF was meant to be this, though I don't think it
| supports everything you'd want. Does NTFS have licensing
| issues though?
| arccy wrote:
| NTFS has serious performance issues, nobody should use
| it.
| dataflow wrote:
| AFAIK that's an incorrect meme that just won't die. The
| performance issues you're thinking of have nothing to do
| with the filesystem itself, but with the I/O subsystem in
| Windows more generally. If you have evidence otherwise
| please share.
| dist-epoch wrote:
| Microsoft itself admits there are performance issues with
| NTFS, which is one reason they created ReFS.
|
| For example ReFS removed the MFT which caused various
| problems.
| dataflow wrote:
| I'm on my phone and this is a longer discussion than I
| can have here, but the performance problems they're
| thinking of and the ones people usually rant about on
| these forums are not the same ones (or same magnitude).
| Before being so confident it's NTFS itself that's the
| issue, try ReFS (and FAT32 for that matter) and tell me
| if you see the performance problems you've encountered
| actually improve a lot. And then narrow down the cause.
| You might be surprised how much of it had to do e.g. with
| filter drivers or other things. And don't forget you're
| still testing one particular implementation on one OS,
| which doesn't say anything about a different one for the
| same filesystem on a different OS.
| dist-epoch wrote:
| I have been running ReFS for many years now on all but
| the system partition. But for reliability/self-heal
| reasons.
|
| The MFT was annoying because if you create 1 mil files,
| and the delete them, the MFT will not be shrunk back.
| dataflow wrote:
| > I have been running ReFS for many years now on all but
| the system partition. But for reliability/self-heal
| reasons.
|
| Have you ever benchmarked it against NTFS? With the same
| exact set of FS filter drivers running on both? How much
| does the performance differ?
| marwis wrote:
| There are tools like voidtools Everything2 and WizTree
| that directly read NTFS from disk device bypassing
| windows FS apis and are blazingly fast (faster than
| find/du on ext4 in Linux).
| BenjiWiebe wrote:
| 'Everything' is caching all the files in memory and
| indexing them. Completely different than find/du on
| Linux.
| e12e wrote:
| zfs?
| mtillman wrote:
| correct. but it's also a management system so perhaps
| they only want a files system? no idea why more don't use
| zfs. especially after the auto expansion update earlier
| in the year.
| adgjlsfhk1 wrote:
| IMO the main reason is that ~90% of ZFS benefits only
| show up with multiple drives which (unfortunately) is
| fairly uncommon outside of servers.
| jajuuka wrote:
| That's a major benefit of ZFS for sure, but I think being
| copy on write is another major benefit for single disk
| systems. ZFS is the only one I know of that has a full
| feature set and is supported on every major OS.
| bombcar wrote:
| Apple almost went with ZFS and Sun pissed off Jobs by
| mentioning it early (IIRC).
| nimbius wrote:
| xfs.
|
| if GPL is a non-starter for you, youre missing the point of
| the open standard. apple already discloses a litany of
| various GPL it ships. XFS would be no different.
| mystifyingpoi wrote:
| > NTFS was only supported well on Windows until recently
|
| I remember using ntfs-3g without any issues on my first Linux
| laptop 15 years ago. So that's not really "recently".
| gjsman-1000 wrote:
| I intentionally excluded unofficial or third party
| software, as almost anything is supported if you're brave
| enough. The quality of said drivers also wildly varies.
|
| Until 4 years ago, nothing was good enough for the upstream
| Linux kernel.
| mystifyingpoi wrote:
| I mean, yeah, you could say that. Something being in the
| kernel is a good benchmark of quality. But IMO open-
| source is different. For instance, Terraform had no
| stable release from 2014 till 2021, that didn't stop
| enterprises from using it on scale.
| mrpippy wrote:
| Apple recently made FSKit a supported/documented API, which
| should allow third-parties to add support for other
| filesystems:
| https://developer.apple.com/documentation/fskit?language=obj...
| duskwuff wrote:
| Is it actually supported and usable now? I seem to recall it
| spending a lot of time in a "half-documented and not actually
| available" state.
| whywhywhywhy wrote:
| 3rd party supporting a file system would be one of the last
| things on a list of all software I'd ever want a 3rd party
| writing instead of the OS maker.
|
| Nightmare to evaluate the options, pure stress testing the
| options, difficult to know if it didn't mess something up.
| Defletter wrote:
| Question, who maintains NTFS support for Linux? Microsoft?
| The kernel? The distros? Genuinely asking.
| LambdaComplex wrote:
| The current ntfs3 driver is developed by a company called
| Paragon, and it's been part of the kernel since 5.15 or
| so.
|
| I was going to add some additional comments about this,
| but then I found that Paragon's website has an FAQ that
| covers everything I was going to say (and more):
| https://www.paragon-software.com/us/home/ntfs3-driver-
| faq/
| KMnO4 wrote:
| The kernel is built with the NTFS3 driver, provided by
| Paragon.
|
| https://www.paragon-software.com/home/ntfs3-driver-faq/
| duskwuff wrote:
| That being said: FSKit is a userspace API. In that respect,
| it's a lot better than filesystem code running in the
| kernel - it can't crash your computer or corrupt data on
| other filesystems, and it's much more tightly sandboxed if
| it gets exploited.
| mbreese wrote:
| Exactly! Third party file systems support in _user space_
| is exactly what I want to see. It seems to me that third
| party kernel code has always caused me problems. By
| moving the FSKit to user-space, I'm quite happy to try
| something, knowing that it won't affect the rest of my
| system.
| coldtea wrote:
| > _3rd party supporting a file system would be one of the
| last things on a list of all software I'd ever want a 3rd
| party writing instead of the OS maker._
|
| Given how many people use FUSE, Paragon NTFS for Mac, and
| similar tools, you're hardly totally representative.
| i80and wrote:
| Third party read-write NTFS drivers took FOREVER to
| become really robust. I remember hearing horror stories
| not infrequently up until maybe a decade or less ago.
| whywhywhywhy wrote:
| > Given how many people use FUSE
|
| What percentage of MacOS users even know what that is. I
| mean I am in the percent but I know it's sub 0.001
| euazOn wrote:
| Well there's at least two of us.
| conception wrote:
| They don't need to know it to use it. I've seen a fair
| number of commercial cloud drive products use it.
| pdpi wrote:
| MacOS users' awareness of a mostly linux centric piece of
| tech is pretty damn irrelevant here. The point is that
| FUSE is a pretty mature piece of technology, and we know
| that it can be used productively without being that
| nightmare scenario you described. There is no reason why
| Apple's FSKit can't be equally successful.
| __float wrote:
| Do many people use macFUSE? I thought ever since the
| license change it's really dropped off.
| mrln wrote:
| There's fuse-t, which uses a local network filesystem in
| the background, iirc.
|
| Edit: but to be fair, that's mostly only relevant for
| unsupported network filesystems like sshfs...
| mihaaly wrote:
| They trust kernel extensions apparently, all of them.
| socalgal2 wrote:
| I'd be happy for VeraCrypt not to have to rely on MacFuse
| which requires I go turn off some very low-level protection
| to even use. It sounds like this makes that possible.
|
| I don't really understand your objection to be honest.
| Drivers for storage are common on other platforms
| 8fingerlouie wrote:
| What would Apple's incentive be to support Btrfs, Ext4, XFS
| or ZFS ?
|
| Btrfs, Ext4 and XFS are all under GPLv3, which may or may
| not be a problem for Apple, but "just in case".
|
| They tried with ZFS, but couldn't strike a deal with
| Sun/Oracle, so instead invented APFS.
|
| Apple already delivers a stable filesystem. It may not be
| "best of breed", but it works, as billions of devices runs
| on it every day with zero problems.
| pxc wrote:
| Thanks for sharing about this! I didn't know, and I like to
| use (or at least play with) some third-party filesystems on
| macOS.
| jraph wrote:
| This article describes a new disk image format (on which a
| filesystem can be put, APFS in the article), not a filesystem,
| or did I misunderstand?
|
| edit: added the word "image", which I apparently forgot to
| type. Mentioning the edition because otherwise it would make an
| answer to this comment difficult to understand.
| crazygringo wrote:
| This is a new disk _image_ format. Not even a disk format.
| For _virtualizing_ a disk.
|
| On which you can put a filesystem, yes.
|
| There seems to be an extraordinary amount of confusion in
| many of the comments, I don't know why.
| hulitu wrote:
| > For virtualizing a disk.
|
| We really don't have enough disk formats in this space. Is
| this bringing something new ? Or is just polluting the
| namespace.
| coldtea wrote:
| > _Is this bringing something new?_
|
| If only there was a whole post available so one could
| find out...
| sitkack wrote:
| Just reading the title, I was like, I hope it is an update
| to encrypted sparse bundles, and it is.
|
| https://developer.apple.com/documentation/virtualization/vz
| d...
| tonyedgecombe wrote:
| Yes, its going to be similar to a .dmg file on the Mac.
| pmarreck wrote:
| Only Mac users IMHO are well-familiar with working with
| disk images. They are not as diverse or well-supported on
| other OS'es, while nearly every Mac app (prior to the App
| Store) was installed by dragging it out of a mounted disk
| image.
| kccqzy wrote:
| Yeah and OP was asking, why was effort spent on a disk image
| format rather than a file system. Seems like a reasonable
| question to ask.
| zymhan wrote:
| Not any more reasonable than asking why they added new
| transparency effects instead of btrfs support
| neuroelectron wrote:
| Can't abstract away your property that way.
| xp84 wrote:
| Does anybody else think that it would make sense for Apple and
| Microsoft to just get in a room and horse trade a few things
| like this, if they cared about user experience? Cross-license
| both APFS and NTFS, and share any internal documentation under
| NDA so that external drives can use modern formats with safety
| features like journaling without locking users in.
|
| Oh wait, I just answered my question.
| pbronez wrote:
| Any chance this will reduce the space needed for major OS
| updates? Those have always been desperately inefficient.
| duskwuff wrote:
| No. Disk images aren't involved in the OS update process.
| happyopossum wrote:
| They are - in that OS updates are delivered in and extracted
| from disk images. Not sure how they could be any more
| involved...
| duskwuff wrote:
| Not this kind of disk image. ASIF is a read-write disk
| image; an OS update would be distributed in a read-only
| image (if it is indeed a disk image).
| srameshc wrote:
| I hope they did something to not load my hard drive with all the
| AI crap and steal the storage.
| platevoltage wrote:
| This ridiculous arms race can't be over soon enough.
| moondev wrote:
| https://developer.apple.com/documentation/virtualization/vzd...
|
| I guess this is the Apple version of qcow2 and friends
| henry700 wrote:
| It's a shame that every new cool
| product/dataformat/cable/cpu/whatever researched by Apple has
| very little (or no) public documentation. Sure, there are lots of
| hackers who can test and reverse engineer those pretty quickly,
| but it's just unnecessary work. I don't know why Apple is so
| revered in hacker circles, to be honest. Not even Microsoft does
| this shit anymore, they're open sourcing a lot of research this
| decade, but they're still seen with extreme distrust. Whereas
| Apple was always secretive and used underhanded tactics, but it
| is still loved.
| frizlab wrote:
| I have a meta question not directly related to the article but
| more about HN itself. I posted this _exact_ link 9h before this
| submission was posted[1]. How is it possible that there is a new
| entry for the submission given the link is the same?
|
| [1]https://news.ycombinator.com/from?site=eclecticlight.co
| wmf wrote:
| Dupes are allowed after some number of hours.
| 90s_dev wrote:
| It depends. I tried posting a few links I came across over
| the past few days, and it just showed me dups but they were
| from days or weeks or sometimes months ago.
| summarity wrote:
| Not sure why this comment is downvoted. Yes, I got
| redirected for a dupe earlier today for something posted 7
| months ago. And even though the content substantially
| changed, it can't be posted again.
| bombcar wrote:
| I seem to remember getting that and having the option to
| post it again. Maybe it's a karma related thing.
| loeg wrote:
| I thought that number was significantly more than 9.
| azhenley wrote:
| I think it is time * (votes+comments).
|
| In practice, if it gets any real amount of votes or comments,
| you have to wait a year to repost. If it doesn't get any
| attention, it can be reposted quickly (though I think it
| should be a day later).
| socalgal2 wrote:
| It seems like, if the link is the same, submitting a dupe
| should just raise the original.
| brudgers wrote:
| My guess is that "fastest gun in the west" might be a bit anti-
| pattern with respect to community.
|
| Because in ye olden times, mild URL shenanigans seemed to have
| been a common hack to bypass more strict dupe detection.
|
| And the community probably doesn't really benefit from
| aggressive karma seeking --back then being first would give you
| a point for every resubmission. [1]
|
| But that's all speculation based on a supposition that what is
| more likely to be submitted by other users is not a better
| criterion for choosing to submit.
|
| But I could very well be wrong and probably am.
|
| [1] and number of submissions is probably at best a noisy
| signal for front page placement and might be negatively
| correlated with curiosity...I mean even here, what Apple is
| doing doesn't stray too far from yesterday's big press release
| by one of the most valuable corporations in the world.
| brk wrote:
| Might be something weird with this domain. Look at the list of
| submissions, yours isn't the first dupe that was accepted in a
| relatively short time window.
| ChrisMarshallNY wrote:
| Doesn't sound particularly useful, if you aren't setting up
| containers.
| burke wrote:
| If Apple would just ship bind mounts and FS/pid namespaces...
| or even just un-break chroot...
| MBCook wrote:
| Unless they can migrate Time Machine to it. The performance
| improvements sound like they might be a real boon there.
| aquafox wrote:
| Whenever I read "conclusion" as last section in an article, I'm
| suspicious that it was written by an LLM/ChatGPT.
| skrtskrt wrote:
| I think this is actually a human struggle - I add Conclusions
| to my blog posts / dev guides because it feels awkward to just
| end with the last step.
|
| But it also always feels like I am just awkwardly restating
| things I just said. It's not a thesis, an article generally not
| complicated enough to need a re-synthesizing of main points at
| the end.
| thierrydamiba wrote:
| I have an unusual way of communicating sometimes that used to
| be quirky and fun. Now I simply get accused of being a bot.
| Before LLMs I never got accused of being a robot.
|
| I think the idea of good writing is soon going to morph with
| writing that doesn't feel like it was made with AI.
| skrtskrt wrote:
| It drives me crazy that em-dashes are supposedly a smell
| for AI now. The em-dash is a great and underused bit of
| punctuation.
|
| I am just glad I am not in college dealing with all the AI
| and faulty AI detection crap happening. Ridiculous false
| accusations of plagiarism were already awful enough before
| this.
| kstrauser wrote:
| Same here. It's almost as if LLMs emit em-dashes because
| the content they were trained on contains them. Wait
| until skeptics realize how often LLMs use the word "the".
| SkyeCA wrote:
| > It drives me crazy that em-dashes are supposedly a
| smell for AI now.
|
| They're an excellent tell for comments written on places
| like HN, Reddit, and other forms of social media. The
| average person (myself included) simply does not write
| very well and I would wager the majority of English
| speakers are not able to properly use an em-dash.
|
| I expect them in books and suspect that's where the AI
| models are getting them from, but those are being written
| largely by professionals.
|
| It's at a point where the moment I see an em-dash on a
| social media post I cease reading it and move on to the
| next.
| reddalo wrote:
| I used to love em dashes. But now I can't use them anymore --
| people will think it's written by AI.
| evantbyrne wrote:
| If you're going to be this superstitious, then you might as
| well lean into it and have a little fun. Better throw some
| herbs into the air and do a little jig for good measure.
| Personally, I'm going to accept that I won't be able to tell,
| because models are trained and prompted to appear human.
| cyberflame wrote:
| Oh awesome! So it's more virtualisation-focused as opposed to
| HFS+ --> APFS migration?
| aroman wrote:
| Apples and oranges. This is a new disk image format. You can
| create an APFS _volume_ in the ASIF _image_.
| AnonC wrote:
| I skimmed through the article, but I have a question that I hope
| someone can answer. I have a sparse disk image created on a NAS
| (which runs Linux), and I use it to backup some stuff (not a VM)
| from the Mac in the native format (the macOS APFS file system).
|
| Would this new format, ASIF, make this faster and better whenever
| I switch to macOS Tahoe? I hope there wouldn't be any gotchas
| with respect to storing this disk image on a NAS.
| benguillet wrote:
| Would that potentially speed up Docker for Mac and others? (since
| it's using a vm underneath). That would address a major pain
| point
| crest wrote:
| Has anyone found the specification for the format?
| ThePowerOfFuet wrote:
| Was this not already a solved problem? Why reinvent the wheel
| other than for vendor lockin?
| kccqzy wrote:
| It's a solved problem in the sense that Apple solved it more
| than a decade ago. (The sparsebundle format was introduced in
| Mac OS X Leopard from 2007. The sparseimage format was even
| older; I saw discussions of using it with Panther.) Apple
| solved it again but made it faster.
| layer8 wrote:
| "Asif" is a fun name for a disk image format. It's as-if it was a
| real disk. ;)
| whycome wrote:
| Andor is a funny name for a tv show
| teaearlgraycold wrote:
| Well, TV show and/or long movie depending on how you look at
| it.
| archagon wrote:
| What blew my mind recently was that I could store an APFS
| sparsebundle on a NAS drive, then mount it over NFS and use it as
| a plain old APFS volume. Despite the filesystem layering, it
| works pretty much like a local volume, albeit with a bit of
| performance degradation. Seems preferable to something like iSCSI
| for using APFS with network storage.
|
| Perhaps this new format would work even better?
| kccqzy wrote:
| Not sure why that would blow your mind, but Apple's old Time
| Capsule basically mounted a sparsebundle over the network too.
| And yes I would also guess this new format would work better.
| archagon wrote:
| My experience with NFS file management has been less than
| stellar, so running a full, virtualized, and performant APFS
| volume on top of it feels like a bit of a magic trick.
| tayiorrobinson wrote:
| The benchmarks are weird to me - the ASIF tests were done on
| M3/4, but for everything else it was done on an M1?
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(page generated 2025-06-12 23:00 UTC)