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A Sparse image is a type of disk image file that can be created under Mac OS X using Disk Utility. Encrypted sparse image files are used to secure a user's home directory by Mac OS X's FileVault feature. navigation Unlike a full image file (.dmg), which takes up as much actual space as the real disk it represents Main page Contents (regardless of the amount of unused space), a sparse image file (.sparseimage) takes up only as much Featured content actual disk space as the data contained within. Current events This can be advantageous when backing up data. For example, assume a user would like to make a Random article backup of a hard disk volume named "INFO" that is 5GB in size, yet only contains 2.5GB of actual search data. While a single layer DVD-R (with around 4.7GB capacity) would be too small to store a full-sized "INFO.dmg" image file, an "INFO.sparseimage" image file will fit. This is because the unused 2.5GB

from the original volume is not actually allocated within the sparse image file. The "INFO.sparseimage"

file will occupy only 2.5GB. interaction Note that if the 2.5GB "INFO.sparseimage" backup on the DVD is subsequently opened and mounted About Wikipedia as a "clone" of the source volume, the Finder will report the clone as having the original 5GB capacity, Community portal with 2.5GB available, but the virtual disk will be "read-only", because the source image file resides on Recent changes read-only media. However, the first-generation 2.5GB "INFO.sparseimage" on a hard drive, when Contact Wikipedia mounted, may have files added to it until the originally designated 5GB capacity is reached. The Donate to Wikipedia ".sparseimage" file will expand in size to accommodate the additional data. Deleting files from the Help mounted virtual volume will not result in a reduction in the size of the corresponding ".sparseimage" toolbox file. However, the size of the image can be reduced when the volume is not mounted. What links here Two limitations are therefore worth noting regarding the use of this image file format: Related changes 1. A customized ".sparseimage" image file can be assigned a larger total capacity than the physical Upload file volume (or HD partition) on which it originally resides. While the virtual volume will seem to make Special pages that capacity available, attempting to exceed the physical capacity of the underlying volume will Printable version result in a disk error: "ran out of space". The ".sparseimage" file must first be moved to a larger Permanent link Cite this page physical disk or partition. 2. As noted above, while mounted ".sparseimage" image files automatically expand to their preassigned limit if and when data is added, they cannot be arbitrarily resized without using additional third-party software tools. A new ".sparseimage" file of the desired size must be created, and the source volume properly cloned onto it. However, when the sparseimage file is not mounted, the .sparseimage file may be resized from the Terminal. The following example resizes a .sparseimage so that it can expand to a maximum size of 50 gigabytes:

hdiutil resize -size 50g MyFile.sparseimage Similarly, a .sparseimage file that has expanded in size but then had files deleted, can be "compacted" to a smaller size with the following command:

hdiutil compact MyFile.sparseimage

Additional information about the hdiutil command may be seen by typing the following in the Terminal:

man hdiutil

Sparse Bundles [edit]

http://en.wikipedia.org/wiki/Sparse_image[23.7.09 13:51:12] Sparse image - Wikipedia, the free encyclopedia

Mac OS X v10.5 (Leopard) introduced the concept of Sparse Bundles[1]. Instead of a monolithic file, a Sparse Bundle is a bundle (directory) that stores the disk image as banded data files in 8M chunks. When you add, modify or remove files in the bundle image, one or more of the band files will change, depending on where your data is stored. This allows backup software (such as Time Machine) to operate more efficiently.

References [edit]

1. ^ Live FileVault and Sparse Bundle Backups in Leopard Mac OS X 10.3 Help , apple.com

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