Q&A: Disappearing disk space

Q I have a 24in iMac which I run with Time Machine backups turned off. Oddly, 228.7 GB of my internal disk space now seems to be occupied by something referred to as ‘Other’. Where has this gone, and how can I get it back?

A The first and most important fact to establish is whether this apparently missing space is in your startup volume, or a different volume in the disk. This is straightforward to discover using Disk Utility: select your startup volume (not the top-level drive, but the named volume underneath that), and look at the capacity given. If this is essentially the same as the disk size, then the missing space is accounted for by files located on your startup volume.

spacediskutilityIf the missing space is on a separate volume, then at least some of it should be the Recovery Partition, or could be a Boot Camp Windows partition. Recovery Partitions should not be that large, and if that were the issue there would be a clear problem with that partition. If from Boot Camp, then you would need to repartition your drive to recover the space, which is the general solution when this missing space is on a different volume.

If the missing space is contained within your startup volume, you need to track the offending files down. The Other category in Disk Utility’s display includes all your Home folder except for photos, audio, and movies, together with everything else that is not in the main Applications folder.

Grand Perspective, showing a breakdown of the space occupied by items within a folder.

There are several utilities that can help in this, including Grand Perspective (free), and DaisyDisk (£7.99 in the Mac App Store). Before using them, try restarting with the Shift key held down to flush the OS X caches, which might help. Then use the tool of your choice to locate where the missing space is.

DaisyDisk, showing a breakdown of the space occupied by items in one folder.

You should be able to identify what it is, hence how you can remove it. The chances are that these are overgrown logs, accumulated temporary files that can readily be removed, or normal hidden files such as Spotlight indexes that have become bloated because of errors.

If the files are in a hidden folder, such as your Home folder’s library, you can use the Finder’s Go to Folder… command in the Go menu, or a maintenance tool, to get at them. General purpose utilities can also provide useful commands to flush most of the standard caches and other hidden files that might be responsible. Be very cautious, though, of ‘clean-up’ or ‘housekeeping’ utilities: sometimes they can remove more than you intend, and can cause distressing problems.

Updated from the original, which was first published in MacUser volume 28 issue 01, 2012.