ASIF Format: Faster Virtual Storage in macOS 26 Tahoe
macOS TahoeS ASIF Disk Image Format Speeds Up Mac Performance
Updated June 16, 2025
Apple’s macOS 26 Tahoe brings a new disk image format, ASIF, poised to revolutionize virtual storage handling on Apple silicon Macs. The new ASIF disk image promises to change that.
Disk images have long been essential for Mac users,facilitating encrypted file storage and virtual machine management. However, performance has been a persistent issue, especially with encryption. Customary encrypted sparse images frequently enough exhibited speeds comparable to older hard drives, even on fast SSDs.
Early testing indicates that ASIF images can achieve read and write speeds nearing a Mac’s internal SSD capabilities. A 100 GB ASIF image on a MacBook Pro M3 Pro achieved unencrypted APFS transfer rates of 5.8 GB/s for reading and 6.6 GB/s for writing. With encryption, speeds only decreased to 4.8 GB/s and 4.6 GB/s, respectively. Similar results were seen on a Mac mini M4 Pro running macOS 15.5,with write speeds reaching 8.3 GB/s.The ASIF disk image format represents a notable leap.
Apple has revealed limited details about ASIF’s mechanics, but the format is designed to be self-reliant of the host file system. ASIF images are marked as sparse files in APFS, growing in physical size only as data is added. A new 100 GB ASIF image might initially use less than 1 GB of disk space. Even after substantial use, the image’s footprint typically remains under 3.2 GB when emptied.
Currently, ASIF disk images are created using the Disk Utility app or the diskutil command-line tool in macOS 26. While straightforward for command-line users, support is absent in earlier macOS versions and the hdiutil tool. apple has not specified which older macOS versions will support mounting and using ASIF images, raising compatibility concerns.
The performance gains from ASIF are particularly beneficial for virtualization. Apple recommends virtual machines transition from older RAW disk images to ASIF, citing improved speed and efficiency in transferring VM files. Unlike sparse bundles, ASIF images consolidate all data into a single file, simplifying management and boosting speed.
Despite these advantages, ASIF creation is currently limited to macOS Tahoe and relies on command-line tools, lacking a dedicated API. Third-party apps and virtualizers will need updates to fully leverage ASIF’s potential. Developers are already exploring the possibilities, with tools like C-Command’s DropDMG expected to add ASIF compatibility soon.
What’s next
The Mac community awaits broader support and more technical details from Apple regarding the new ASIF disk image format. The improved disk image performance promises benefits for users and developers alike.