Mac OS 26 – Tahoe – introduces a new disk image format

Disk images have been valuable tools marred by poor performance. In the wrong circumstances, an encrypted sparse image (UDSP) stored on the blazingly fast internal SSD of an Apple silicon Mac may write files no faster than 100 MB/s, typical for a cheap hard drive. One of the important new features introduced in macOS 26 Tahoe is a new disk image format that can achieve near-native speeds: ASIF, documented here.

macOS Tahoe brings a new disk image format – The Eclectic Light Company

https://eclecticlight.co/2025/06/12/macos-tahoe-brings-a-new-disk-image-format/

TIL: disk images had write speed bottlenecks. I suspect they made these improvements because of their path to support containerization.

Conclusions

  • Where possible, in macOS 26 Tahoe in particular, VMs should use ASIF disk images rather than RAW/UDRW.
  • Unless a sparse bundle is required (for example when it’s hosted on a different file system such as that in a NAS), ASIF should be first choice for general purpose disk images in Tahoe.
  • It would be preferable for virtualisers to be able to call a proper API rather than a command tool.
  • Keep an eye on C-Command’s DropDMG. I’m sure it will support ASIF disk images soon.

Exciting.

#containerization #containers #diskImages #mac #macOs #osX

macOS Tahoe brings a new disk image format

ASIF disk images are new in Tahoe, and promise to be space efficient, as they’re sparse files, and almost as fast as the disk they’re stored on. Ideal for VMs and general use.

The Eclectic Light Company
🍏🖥️ Introducing macOS Tahoe! Now you can enjoy your disk images moving at the speed of a *cheap hard drive* on your shiny Apple silicon Mac. Because who doesn't want their blazing fast SSD reduced to the processing power of a potato? 🚀🔋
https://eclecticlight.co/2025/06/12/macos-tahoe-brings-a-new-disk-image-format/ #macOSTahoe #AppleSilicon #diskImages #SSDPerformance #techNews #HackerNews #ngated
macOS Tahoe brings a new disk image format

ASIF disk images are new in Tahoe, and promise to be space efficient, as they’re sparse files, and almost as fast as the disk they’re stored on. Ideal for VMs and general use.

The Eclectic Light Company
DART - Directory Art Importer for the Commodore 64 - The Oasis BBS

A Linux-based command-line tool for importing directory art into D64 disk images, developed by Sparta/Genesis Project.

The Oasis BBS
Commodore D64 Files: Everything About Them You Never Wanted To Know - The Oasis BBS

Join Commodore History for a deep dive into the D64 file format. Learn how the disk images work, what they store and how they're structured.

The Oasis BBS

Disk image archive and info resource for the Sanyo MBC-550 PC "compatible" from 1982. It's an interesting clone that features better-than-CGA 640x200 resolution 8-color graphics, ending up with a few unique titles, as such.

http://eriscreations.com/index.php/sanyo-mbc-550-vintage-computer-fan-site/sanyo-disk-images/

#DOS #PC #vintagecomputing #retrocomputing #vintagecomputers #gaming #diskimages #Sanyo #MBC550 #Michtron #TimeBandit #CGA

"A computer file system shouldn't lose data, right? Tell that to #Apple" • TheRegister.co.uk

"Apple's recently revised file system, APFS, may lose data under specific circumstances, a maker of macOS backup software is warning.

In a blog post on Thursday, Mike Bombich, creator of Carbon Copy Cloner, says that APFS sparse disk images fail to accurately track available free space, thereby allowing storage operations to continue when space to store the data isn't there."

https://www.theregister.co.uk/2018/02/16/apple_file_system_bug/

#bugs
#diskimages
#dataloss
#computers
#insight
#backup
#ITstrategy