MacOS – How to fix Disk Utility, About This Mac, and Finder that disagree on hard drive space usage

disk-utilityhard drivemacos

Has anyone seen this issue and know how to fix it?

Look at the free space reported by running "Get Info" on my hard drive (Macintosh HD) in the Finder, "About This Mac" from the Apple Menu, and Disk Utility.

Running on an early 2011 MacBook Pro OS X 10.7.3.

Screenshot of Finder, System Information and Disk Utility

Disk Utility shows:

  • 108.31 GB (108,311,060,480 Bytes) available
  • 390.94 GB (390,937,042,944 Bytes) used.

Finder shows:

  • 206.43 GB available
  • 292,816,503,508 bytes used (292.82 GB on disk).

System Information shows:

  • 108.44 of 499.25 GB free.

Best Answer

Most of the difference you're seeing is due to Time Machine's "Local Snapshots" feature. When Time Machine is turned on but the backup device isn't available, it backs up to the local volume. The space used for these local snapshots is counted as "in use" by Disk Utility and System Information, but not the Finder (see the Disk Space considerations section of this article). While the space for backup actually is in use, it'll be freed automatically when needed (i.e. when the volume gets above 80% full), so the Finder counts it as being available.

In your particular case, the space System Information lists as being used for "Backups", 98.36GB, is very close to the difference in free space listed by the Finder vs. the other two. The Finder's 206.43GB free - 98.36GB of backups = 108.07GB actually free; compare to System Info's listing of 108.44GB free and Disk Util's 108.31GB. I'm not sure what the rest of the difference is (maybe they looked at the disk at slightly different times? Or they may be counting volume structures a bit differently?), but it's very small.

Finder shows:

  • easily, the truth for JHFS+ volume Macintosh HD
  • optionally, the truth for mtmfs volume MobileBackups

Hint: with local snapshots enabled in Time Machine, in Finder you can go to /Volumes/MobileBackups then get info.

Results of a one-line command show that for some purposes, MobileBackups is treated as a distant file system: 

qlmanage -m disks | grep MobileBackups && mount | grep MobileBackups

As Disk Utility is oriented to local file systems, we'll probably never see MobileBackups as a separate volume in that context. There are degrees of simplification in Disk Utility, even when debug options are chosen.

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