Apple introduces the Asif disk image format in macOS 26 Tahoe for faster virtual storage

Apple's ASIF format in macOS 26 Tahoe offers virtual storage at near-SSD speeds on Apple silicon, revolutionizing disk image performance.

: Apple has introduced the ASIF disk image format in its macOS 26 Tahoe update, promising speeds almost equivalent to native SSD performance. Traditional UDSP images suffered from poor performance, often limited to under 100 MB/s, but ASIF enables read/write speeds as high as 5.8 GB/s reading and 6.6 GB/s writing. Even when encrypted, ASIF maintains high speeds, only slightly reduced. This development prompts a shift from traditional formats like RAW and sparse bundles, particularly benefiting virtual machines through improved speed and efficiency.

In June 2025, Apple unveiled the ASIF disk image format with the release of macOS 26 Tahoe, aiming to revolutionize how virtual storage is handled on Apple silicon Macs. Traditionally, disk images used for various tasks like encrypted file storage and virtual machine management have been plagued with performance issues, struggling to surpass 100 MB/s. This significant update appears to tackle those historical limitations by nearly matching the performance of native SSDs, which is a landmark improvement.

The ASIF format has already demonstrated its potential through benchmarking tests conducted on hardware like the MacBook Pro M3 Pro. This format achieved an impressive 5.8 GB/s in reading and 6.6 GB/s in writing unencrypted APFS transfer rates. Even with encryption active, the image format maintained high performance with read and write speeds measured at 4.8 GB/s and 4.6 GB/s, respectively. Comparable speeds were recorded on different Mac devices, indicating a consistent improvement across Apple's lineup, with write speeds even reaching 8.3 GB/s on a Mac mini M4 Pro under macOS 15.5.

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Despite its promising performance, Apple has not released detailed specifics about ASIF's underlying mechanics but assures that the format functions independently of the host file system's capabilities. ASIF images, categorized as sparse files in APFS, optimize storage utilization by expanding in physical size only with added data. Moreover, a 100 GB ASIF image could initially occupy less than 1 GB of disk space, even after extensive use, keeping its footprint economical.

The creation of ASIF images is currently limited to the Disk Utility app or diskutil command-line tool in macOS 26, and support for older macOS versions and third-party applications remains uncertain. This circumstance necessitates adaptation from software firms to fully leverage the new format's capabilities. Nonetheless, the anticipation for this next-generation disk image format remains high, especially among developers focusing on virtualization and high-speed storage utilization.

Apple's move to emphasize ASIF utilization is particularly advantageous for virtualization practices. It offers a singular file format in contrast to earlier formats like sparse bundles, which inherently simplifies storage management while augmenting operational speed. This change underscores ASIF's significance in the technology ecosystem as virtual machines evolve to meet greater performance demands from users. Third-party tool developers, like C-Command's DropDMG, are already working on integrating ASIF compatibility, which suggests a broader adaptation could happen in the near future.

Sources: TechSpot, eclecticlight.co, developer.apple.com

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