Leopard Disk Space – Fix ‘Not Enough Free Space’ Error on OSX 10.5.8

Both sparse disk images and the newer sparse bundle disk images intentionality do not reap/reclaim space until they need to. This is especially so for a sparse bundle - which is designed to reduce the network transfers when the image is stored on a network share. It certainly speeds up normal read/write operations since the system can assume compact won't happen when the files are changing. When you check things in disk utility, it perhaps sees that space could be reclaimed and does that for you. You are correct, that in normal use, it ends up with you using more space than if you simply put things on the normal file system.

You could convert your storage to a normal sparse image to get more traditional freeing of space when you delete files stored within the disk image.

Certainly read the first two paragraphs of the man page for hdiutil.

You can of course kick off a manual compact operation with:

• hdiutil compact /path/to/sparsebundle.dmg

Take a look at Time Machine, it may be keeping local snapshots.

From Apple Support:

Because Time Machine removes local snapshots as needed, Finder and Get Info windows don't include them in their calculations. To see how much storage space local snapshots are using, choose About This Mac from the Apple menu, then click Storage. The space used by local snapshots is labeled Backups.

You can disable them, but they get automatically deleted if you need space:

• If less than 20% of the total storage space on your startup drive is available, Time Machine removes local snapshots, starting with the oldest, until you have more than 20% free space.
• If less than 10% or less than 5GB of storage space is available, Time Machine removes local snapshots more quickly. When only one snapshot remains, Time Machine stops creating new snapshots. As free space increases, Time Machine at first replaces the previous snapshot with a new one, then eventually resumes creating snapshots as normal.