If you have a laptop with a small hard drive, or a Macbook Air with a small SSD drive, you might be interested in knowing why you are running out of space.
Recently, I kept getting warnings that the 240 GB SSD drive in my MacBook Pro had less than 15% free space. First, I should explain that my MBP is non-standard since I modified it last year by replacing the optical drive with the SSD thus giving me a very fast SSD drive for the system and applications, and the standard 500 GB hard drive for all my large files. I thought that this system would give me the best of both worlds, and for a while it was.
But then I started getting these warnings and I started looking for culprits that were stealing my space. I started with “About This Mac” which told me that I had about 70 GB free space on my 240 GB drive. Then I used “Show Info” in the Finder and it said I had 140 GB free – a big difference!
Then I got a little more sophisticated in my sleuthing and ran several apps that help you see what’s happening on your drives. I ran OmniDiskSweeper, DiskWave, and GrandPerspective. All three of these free apps gave roughly similar results — they all said that I had used about 80 GB and had 70 GB free space. It’s been a long time since I was in math class, but I’m pretty sure that 80 + 70 = 150. And 240 – 150 = 90! Who stole my 90 GB.
I admit that I was baffled for a while until I started turning to my old friend Google and discovered a little secret. Apparently, starting with Lion, Apple added a new “feature” for laptop users using Time Machine for backup. Unfortunately, they didn’t tell anybody about this, or at least I never knew about it.
If you have a laptop, are running Lion or newer OS X, and use Time Machine, then every time you start your Time Machine backup without a destination drive all your data is copied into a secure (and hidden) folder called “.MobileBackups”. If you travel a lot and want maximum protection, then this can be a useful feature. But it eats up drive space like mad. In my case it gobbled up 90 GB!
Once you know what to look for you can actually find this in the About This Mac Information screen. Go to the “About this Mac” section in the Apple menu, then choose “More Info” and then click “Storage.” In here you will see a purple/pink section called “Backups” that should be the size of the difference between the Finder’s reported disk availability and that of the other other utilities.
Luckily this feature is easy to disable.
Open up the Terminal Application and type
sudo tmutil disablelocal
The hidden folder will be deleted and soon you will have recovered all the missing space. If you want to learn more you can find a number of discussions on line such as this one on Apple.
As always, make sure you have a current backup of your system before attempting this fix.