Why is my HD showing full - can't see what is taking all that space

My friend has a 24" IMac with a 680GB hard drive. Using OmniDriveSweeper to see how big and where files are - it seems the home folder has about 13 GB for all the users. Why does the disk Utility show that the HD as nearly full, and only about 2 gb of free space out of 680 total?

Where are all the 600GB of files? Time machine is on. There are 2 large external drives but they are not full.

Any help would be appreciated. Floyd

Don't know OmniDriveSweeper, but have seen the interface and doesn't really tell you a great deal. So if you download DaisyDisk and use it for free to see the Files, you will get a better representation of where your space is going. This is a great App, and the paid version, lets you delete right in the App.

You don't give us much to go on really. What OS are you running on the iMac ?? Would be a good start.
But to give you a little help, if you have say 200GB of files on the iMac HD and TimeMachine is interrupted while its doing a Backup, it will store what is like a SwapFile and its called something like (MobileBackUp) on the iMac, until it can finish the Backup, and sometimes if it is left too long, that File will be left on the HD, and if this has happened a couple of times, it won't take long to fill up the iMac HD.

Saying that, 2GB free seems wrong to me. You should (or your friend should) have a good idea what is on the Mac, like Music, Movies, TV Shows, Pictures and documents, so you should have a idea of how much it should be using and how much is free.
If you did only have 2GB free, you would be getting the SBOD continuously, because you need at least 10% free space for your Mac to function in some way. 10% is the bare minimum and 20% is what you aim for, to have the mac run at optimum.

So try Repairing Permissions on your HD via Disk Utility. Open it up, select the Macintosh HD in the left column, then First Aid and Repair Permissions. Once finished restart the iMac and see what it says now ?? Any changes ??

Tatt, Thanks for reply. Just upgraded to Mavericks yesterday. Have not done the most recent update to 10.9 because of the low disk space left. We did repair permissions today but did not restart. The mystery is - Finder and OmniDriveSweeper show only 13 GB of files on the HD. Disk Utility says HD almost 100% full. No errors yet at start up.

Will restart and check the Time Machine tomorrow. Where do we find those interrupted backups on the iMac?

Have a read of this thread in the Apple Forums about the .MobileBackups. I got the wording wrong, as they are Local Snapshots not a swapfile, but you will need to show Hidden Files to be able to see it.

You can do this with the Daisy Disk App, if you scan as Administrator, but you need to pay the $9.99 to do this.
BUT, you can do this in Terminal by copy and pasting this in and hit return : then type in and hit return.

The first line lets all the hidden files on your Mac visible and the second one, relaunches Finder, and you need to do that to let the files be shown.

.MobileBackups will then be in /Volumes and you will have to Right Click or ⌃Click (control click) to bring up the Contextual Menu and Put it in the Trash.
Remember once its there, you will have to empty Trash to get the HD Space back.

Once done, reverse the hidden files by Return and Return

HTH some, but really first, you need to work out, IF there is these .MobileBackups doing the Space Hogging, and to do this, you need a App like Daisy Disk, that will allow you to scan as a Administrator so you can see the Hidden Files. To be honest, for the price of 2 coffees, Daisy Disk is worth its weight in Gold. It has saved me so much time, and headaches, because with the Paid version, you can see the Hidden Files, and Delete them from the App, without having to try and find them yourself.

There are others out there, and have tried others, but DD, is the one I came back too

Good luck.

We got Daisy Disk and found that the hd was full with a large file called External Hard drive or something. So time machine must have tried to backup in the wrong place. We could not delete it so did a clean install of the OSX. Thanks for your assist and advice.

It's hard to say for sure without knowing the exact name of the file but I doubt that was from Time Machine. IIRC those files are called .Mobile backup as member TM suggested, Have you had a problem waking the computer recently or have it rundown on battery to very low? That might be the name of the image file created when the Mac shuts down due to low battery.

Sly, The machine is a 640GB, 24" iMac some 4 or 5 years old. Not sure. That problem file or sparsebundle was about 620 GB. Could not trash it because - not sure why. The owner dragged many programs and files to his external drives trying to create free space on computer HD. Did not know what he was doing. Everything got messed up. Easiest thing to do was start over.

In that case you are probably right. It was a good time to start fresh. If the owner is anything like I am there was probably stuff on there that had not been used in quite some time.

I have literally seen people use Time Machine to try and back up their boot drives -- to their boot drive! It would not surprise me at all if the owner mixed up the "target" and "destination" they wanted to back up when using some other type of backup program (it's pretty hard to do that in Time Machine). Probably something simple like that.