Disk space usage on MacBook Air 256 GB

Are you using Time Machine? It stores backups locally until you connect the Time Machine backup disk.

There are several utilities that can be useful to determine what is occupying so much space. One is called WhatSize, another is OmniDiskSweeper. As I recall ODS is free, WhatSize is about $12.

If you need more insight go to Apple Support contributor Pondini's website:

OSX Tips

Where did my Disk Space go?

Movies take up an incredible amount of storage. 1 hour=30-40GB. If you are editing videos it can use even more space until you move the "clips" off your harddrive.

Another culprit may be the Safari cache file.

1. Quit Safari
2. Delete everything in ~/Library/Caches/com.apple.Safari/
3. Empty Trash

I'm still betting on the Time Machine backups being the issue. Apple sometimes "adjusts" reported free space to try and remove this space, though I've seen it get (temporarily) fouled up about this number. So, for instance, Finder does not count such space as used, but Disk Utility will show it as used.

Those backups are written to "/.MobileBackups" which (kind of) shows up as the "MobileBackups" drive you will see from time to time. Although items are written out to it and some deletion compression takes place, like your external Time Machine the general rule is that this thing will continue to grow until it (eventually) fills all available space. That is by design.

The MobileBackups disk you see in OmniDiskSweeper is the mounted version, and it doesn't appear you will get useful information if you "size" that volume. However I believe you can get the "real" size of the MobileBackups from a couple of places.

Officially, About This Mac->More Information and then Storage will tell you about the backups on your flash drive. That's *usually* correct, though I've seen it get lost on the machine I'm writing this on. I suspect that's because the machine had been set up using Migration Assistance from a MacBook Pro that had been running Lion for a while and some of that information may have "tainted" the starting point. Now the system appears to have finally figured out the real space used :-) .

I'm not sure it's more reliable (since now everything appears to work fine), but you might also get some information if .MobileBackups is involved by running the command in Terminal to show the size of that directly (Finder won't show because only root has permission to look at it).

I first fired up Terminal to get a command prompt. From that prompt I entered the following:

sudo du -sk /.MobileBackups

You will be asked for your password to authorize the command, but by the Terminal (not the standard OSX dialog).

When it ran (took a short time) it output the following:

Which basically agrees with the 2.8GB of backups that About This Mac's More Information screen comes up with now. And which Finder totally ignores and treats as not used.

If your drive has as much free space as you expect it should have and either you've had the machine for a while, or you've downloaded and deleted a buch of videos in a directory that's not excluded from Time Machine's backup routines, I could see those "there but not really" files (at least as OSX seems to view them) easily growing to be a pretty good size. As I noted, if this is the problem OSX will kick parts of that backup off the drive as more space is needed--it's holding them there "just in case" you might want to restore them.

Have you actually had OSX complain about not having enough free space on the boot drive?

What I have found with Lion is that trying to reconcile various utilities views of free drive space can quickly drive you crazy :-) . The cause always seem to involve accounting for that mobile version of Time Machine backups.

You may need WhatSize, as Pondini says it is the only "visual" utility that enables you to see everything at once. It may be the "false volume" which is in the normally hidden /Volumes directory.

As he notes that version of WhatSize must be downloaded from its website, not the App Store.

Let me jump in because I am having a similar problem. I have now bought two disk utility programs, WhatSize and DiskDaisy, and get the same results from both, and a similar problem as the OP.

It's a Macbook Air with a 220 Gb partition

The OS reports 165 Gb used and 55 Gb available.

I run both utilities and get the same results. Adding up all of the files while running as Administrator, they total 105 Gb NOT 165 Gb.

Where did my 60 Gb go?

Similar issue.

The key number is that 7 gig in Private.

From the OS X tip link this contains:

"System Work Files, mainly Virtual Memory Swap files and the sleepimage file on laptops.

From a Finder menubar, select Go > Go to Folder and type /var/vm in the prompt (you must include the slashes).

You should see the following files: •swapfile0 and perhaps one or more swapfile1, swapfile2, etc.

These are used by OSX when your Mac needs more RAM (memory) than you have, so it "swaps" the contents of sections of memory out to disk temporarily so another process can use it.

These start at 67 MB, then get larger if more are needed. If you have a large number of them, and the total size is several GBs, you may need to consider getting more memory and/or running fewer applications at the same time, or you may have an app with a "memory leak" (not releasing memory that is no longer needed).

Restarting your Mac will delete all but the first one or two, at least for a while.

•sleepimage is used on laptops to hold the entire contents of your RAM so it can be powered-off during sleep. It is read back in when your Mac awakens. It should be the same size as your installed RAM."

Simply restaring my machine cleared two gig of space - not done it in a while so that was a good start.

The other big offender (and not that obvious unless you scan with DaisyDisk or something) is locally stored IMAP mail downloaded from Gmail etc.

This is stored in what is now hidden directory under Macintosh HD/your_user_name_/Library in a directory called Mail.

In my case it turns out I have a 13.5 GB [Gmail].mbx

That's a big file, and one you can't normally see. The decision I suppose I have to make is whether I need the account to download a local copy to my MacBook Air (I already have a copy on my desktop) and stick to using a web client... or ...?

Hope that helps.

(BTW DaisyDisk is very good and worth having)

Well I figured it out, thanks to the link above to tips of disk usage. It turned out that I had 65 Gb of orphaned files on the disk. The OS will show that space as used, but all of the disk managers don't see the files when they are counting up space.

Running a disk repair from the restart (holding down command-R when restarting) fixed the file system and recovered the space for me.

Hi,

I have faced similar issue. Turn off Time Machine. Back up space that was been used is simply cleared after that (you may need to restart your Mac). Then, check it out on "about this Mac". You will not loose yuor previus back up from Time Machine, but from that on, you must make sure to remember to open Time Machine whenever you want to back up your data.