sparseimage

A sparseimage is a type of disk image format used on macOS that represents a virtual disk whose allocated storage grows as data is written. It is stored as a single file on the host filesystem, commonly with the .sparseimage extension, and can be created and managed with the hdiutil utility or Disk Utility. When created, the image has a specified maximum size, but only the data actually written into the image consumes physical space on disk. As content is added, new blocks are allocated up to the maximum size, allowing substantial space savings when the image is sparsely populated.

Mounting and use are similar to other disk images: the image appears as a mounted volume and can host a filesystem, files, and applications. Encryption can be applied at creation time or added later, providing protection for the contents. The image can be resized to increase or decrease its maximum capacity, subject to available disk space and filesystem constraints.

Sparseimage is distinct from sparsebundle, another macOS disk image format. A sparseimage is a single file, whereas a sparsebundle stores data in a directory-based bundle divided into bands; sparsebundles are often used for network backups due to their resilience to partial transfers.

Common uses include creating compact backups, portable containers for transporting data, and staging areas for large datasets without consuming disk space upfront. Limitations include potential performance overhead from on-demand allocation and the need to ensure sufficient free space during growth or resizing. Overall, sparseimage provides a space-efficient way to manage large disk images on macOS.