macOS Tahoe Brings a New Disk Image Format

Apple's macOS 26 'Tahoe' introduces a new disk image format called ASIF, designed to dramatically improve performance over previous formats like UDRW and sparse bundles -- achieving near-native read/write speeds for virtual machines and general disk image use. The Eclectic Light Company reports: Apple provides few technical details, other than stating that the intrinsic structure of ASIF disk images doesn't depend on the host file system's capabilities, and their size on the host depends on the size of the data stored in the disk. In other words, they're a sparse file in APFS, and are flagged as such.

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 virtualizers 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.

Read more of this story at Slashdot.