Disk Utility

Disk Utility

Developer(s)	Apple Inc.
Stable release	11.1 (252.4) / December 15, 2008
Operating system	Mac OS X
Type	Utility
License	Proprietary
Website	support.apple.com/guide/disk-utility/welcome/mac

Disk Utility is the name of a utility created by Apple for performing disk-related tasks in Mac OS X. These tasks include:

• the creation, conversion, compression and encryption of disk images from a wide range of formats read by Disk Utility to .dmg or—for CD/DVD images—.cdr, which is identical to the .iso format;
• mounting, unmounting, and ejecting disks (including both hard disks, removable media and disk images);
• enabling or disabling journaling;
• verifying a disk's integrity, and repairing it if the disk is damaged (this will work for both Mac compatible format partitions, and FAT-32 partitions with Microsoft Windows installed);
• verifying and repairing permissions;
• disk erasing, formatting, partitioning and cloning;
• secure deletion of free space or disk using a "zero out" data, a 7-pass DOD 5520-22 M standard, or a 35-pass Gutmann algorithm
• adding or changing partition table between Apple Partition Table, GUID Partition Table, and master boot record (MBR);
• creating, destroying, merging, and repairing RAID sets;
• restoring volumes from Apple Software Restore (ASR) images;
• burning disk images to CD or DVD in HFS+ format;
• erasing CD-RWs and DVD-RWs;
• checking the S.M.A.R.T status of a hard disk.

Disk Utility functions may also be accessed from the Mac OS X command line with the diskutil and hdiutil commands.

Disk Utility was updated with Mac OS X v10.3. Prior to v10.3, the functionality of Disk Utility was spread across two applications: Disk Copy and Disk Utility. Disk Copy was used for creating and mounting disk image files, and Disk Utility was used for formatting, partitioning, verifying and repairing file structures. The ability to "zero" all data on a disk was not added until Mac OS X 10.2.3

Further changes introduced in 10.4.3 allowed Disk Utility to be used to verify the file structure of the current boot drive. However as Apple notes in their public knowledge base doing so can sometimes yield false error messages.

Mac OS X v10.5 Leopard added the ability to create, resize, and delete disk partitions without erasing them, a feature known as live partitioning.

In versions of the Mac OS prior to Mac OS X, similar functionality to the verification features of Disk Utility could be found in the Disk First Aid application. Another application called Drive Setup was used for drive formatting and partitioning, and the application Disk Copy was used for working with disk images.

Errors

Erase free space is one of the functions of the disk utility. It ensures that all files deleted using the empty trash option, or any other non-secure file deleting tool, will be removed forever as if secure empty trash were to have been used in the first place. This process is the same as formatting an entire disk, except that the used disk space will be left untouched. This is an important tool for two reasons: 1. Files deleted using the empty trash option, as opposed to the secure empty trash, are not removed and can be recovered with the appropriate software and 2. Once empty trash is used there is no way to go back and use the secure empty trash to completely erase those files without using erase free space through the disk utility. Because a well known, potentially destructive, and easily occurring error can happen during the erase free space process, the process for recovering from this error should be noted.

Sometimes, when using the erase free space function of Disk Utility, the process will be interrupted by a crash, hang, power outage, or general problems with the power supply. Should this happen, you’ll find that your disk has suddenly lost the majority of its free space and nothing you do in the GUI will show you where it is. No amount of checking the disk will bring it back, because it’s not a catalog problem.

Disk Utility accomplishes the erase feature by creating large sparse image files in a preset directory. It then deletes them with the srm tool (secure remove) and an overwrite pattern of your choice. If Disk Utility is interrupted, this sparse image is left on the disk just taking up space. Starting another free space erase session makes another file, instead of cleaning up the previous one. In some cases the sparse image can take up 100% of your computer's free space. In this instance you will not be able to begin another erase free space process until you have removed the sparse image. There are no checks in Disk Utility for cleaning up this failed process, so it must be done manually.

The files are created in /var/root/Library/Caches/TemporaryItems and are sequential variations of the name EFTFile1.sparseimage. Simply remove these files (as root) to reclaim your free space and then start the process again to finish the task.

sudo rm -f /var/root/Library/Caches/TemporaryItems/EFTFile.sparseimage

This process only works for a Boot disk. If you are using a non boot disk, such as a second internal hard drive or an external hard drive, the sparse image(s) will be located: /Volumes/YourVolume/.TemporaryItems/folders.UIDNumber/TemporaryItems/

“YourVolume” is the name of the volume being erased, and “UIDNumber” is the UID number of the user performing the erase.

Some users have reported that they have had no success using this process. These users have been able to reclaim 100% of their free space by shutting down their computers, rebooting them, then emptying the trash. The sparse image should, after a reboot, be located in a recovered files folder in the trash. Deleting the file will recover all lost disk space.

See also

• Logical Disk Manager
• GNU Parted
• diskpart
• fdisk
• cfdisk

References

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Burn .ISO file with Disk Utility