Sparse Image¶

Version 4.3.2 introduces support for encrypted Apple sparse disk images. The main advantage of sparse images is that the diskspace used is not determined by the size (capacity) of the disk image (as with most other disk images) but by the size of the files contained in the disk image. The consumed diskspace grows dynamically when you add files to the disk image.

More information on this disk layout is available here and here.

Important: please note the subtle difference between sparse bundle disk images and sparse disk images. The former are documented here. Sparse disk images are self contained in a single file, whereas sparse bundle disk images are, like the name implies, bundles being a directory containing multiple sub-files.

UDSP vs. ASIF¶

Before macOS 26, Sparse Image referred to the UDSP format. In macOS 26, Apple introduced the Apple Sparse Image Format (ASIF), a new format carrying the same 'Sparse Image' name, replacing the now deprecated UDSP format. Disk Decipher 6.2.4 and higher supports the ASIF format too.

Limitation¶

Sparse disk image support is currently read-only for both UDSP and ASIF. As UDSP is deprecated, write support will likely be added for ASIF only. To do so, more knowledge of the ASIF binary specification is needed.

If you have more information on the ASIF binary specification, please open an issue or pull request.

Please upvote this feature request if you need write support.

Create ASIF sparse image¶

You can easily create a new ASIF sparse disk image on macOS 26 or higher by using Disk Utility. Just select File -> New Image -> Blank Image and use settings like

Or using a command like this in Terminal:

$ diskutil image create blank --format ASIF --size 1g --encrypt -fs MS-DOS test.asif

Create UDSP sparse image¶

You can easily create a new sparse UDSP disk image on macOS 15 or lower by using Disk Utility. Just select File -> New Image -> Blank Image and use settings like

Or using a command like this in Terminal:

$ hdiutil create -type SPARSE -size 1g -layout NONE -fs FAT32 -encryption AES-256 test.sparseimage