Where can I find the files using up my external hard drive?

To obtain information on all three hard drives use I just Apple "I" it to Get Information about that particular disk. Which of the three disks do you want to know the free space?

iMac disk - 159GB used, 840GB available

Time Machine disk 226GB used, 23GB available

iTunes disk 68GB used, 51GB available

Should I follow one of those links?

I just ran Disk Utility and it says all is fine. I believe I did check the 250 when it was blank by seeing it's available space with Get Info, but that was all that I did. I'll try using the utilty and terminal procedure you advised earlier, and see what we have.

I also wanted you to know I posted back in June trying to resolve issue under the discussion listed:

"How can I change time machine settings?"

Not really. Back in June I was given advice on how to use the Time Machine software I have used on two different Apple computer without any confusion using it's simple interface. I may have erased the 250GB at that time and did the fresh backup...I don't remember.

Right now, I'm trying the first run of OmniDiskSweeper without using Terminal from the Finder / iMac. The 120GB information was identical. Currently, it's working on the 250GB processing / sizing.

Okay here's the results from running OmniDisk from the Finder on the iMac:

120GB/iTunes Drive:

68.2GB for the iTunes folder and all the remaining items are small-between 6MB to 536KB

250GB/Time Machine Drive:

7.0TB for Backups folder and remaining items again are even smaller 800KB to 4KB

1TB/iMac:

95GB Users

26GB Library

15GB Applications

4GB System

1MB private

600MB usr

175MB System Folder and then again, the remaining items run smaller ranging from 15MB down to 4KB

I didn't make any deletions, but I did screen shots for all the information. I believe I may not have gone far enough into it's interface and information to obtain detailed info. One thing that is somehow wrong is the figure of 7.0TB on the 250GB Time Machine Drive, which by the way was the only disk which took a very long time. Can you see anything sticking too that may be an issue?

Yeah - sure I was already preparing to do that and to my surprise, the iTunes Disk had not been excluded from Time Machine. We may have figured it out. Thanks. I'll get back to you on these results.

Okay...I have some more information and perhaps we are getting closer. On the 250GB, first I went into that disk and used Disk Utilty to re-format it once using Mac OS Extended (Journaled) then a second time, zeroing it out. I did a screen shot to review if needed, and both times it looked perfect...249GB available. Then I went into the Time Machine preferences to get ready to backup again, and it had not excluded the other external 120GB with iTunes so I excluded it. I may has previously, never noticed in that screen that it takes a bit of time for it to calculate the information to save. I may have just clicked on it quickly without reviewing it first. Today I did, and gave it time to calculate. At one point the actual 250GB itself, showed up and I excluded it too like the 120GB. After it finished, the calculations are still it wrong - claiming it has a 200GB backup when the iMac either contains 150GB (based on when I do Get Info) on it or from OmniDisk which calculated about 100GB. I have not allowed Time Machine to do a backup yet, until this discrepancy can be clear.

One thing that I thought I had seen or reviewed previous on the Time Machine settings was my home folder - I could be wrong but wanted to mention that. Another little tidbit to ponder an well is that I have a files of icons that I use for the Hard Disks, and a few folders where I Get Info on the Icon and on the destination and just cut and paste. I did that today to the 250GB after zeroing, but while I was in the Time Machine settings the change was deleted and neither the manufactures icon was there nor mine, and it has the default blue-green one the software uses. I know, because my sister's is that way on her system-unchanged.

Feedback?

I completely shut down the whole system...iMac and the two externals. Waiting a bit, and then brought it all back up and just for ha-ha's did Get Info and ran OmniDisk again on the 250GB and it still looks good - totally clean. I did Get Info on the iMac and ran OmniDisk on it and they both agree on 150GB. When I went to Time Machine it's said 200GB so I completely cleared it out of any settings...went back in and made sure the backup was correct and it now is calculating correctly-150GB. There was something in those settings that were incorrect previously. I haven't started it yet.

Once I begin this new backup with Time Machine do I have it correct that the most will ever contain is 150GB, the capacity of the iMac? I've never seen any backup larger than the original...but just wanted to make sure this software isn't doing something I don't understand...hopefully I will not see it creeping up to 500GB like when we started.

Just wanted to let yoo know that after the work that we did was complete, and Time Machine backed up correctly I went ahead and upgraded to Mountain Lion. Once again, everything that happened before happened again. I posted on to OS 10.8 forum:

https://discussions.apple.com/thread/4587209

Everything is exactly as before. The icon, the indication the 250GB is holding a TB, etc.

Maybe I have to delete it again and start over.