Hard drive space disappears. Can't account for missing disk space.

You can start by opening the Console application in your Utilities folders and examining the console and other logs for any abnormal activity. Next open Activity Monitor and look for any abnormal information in the processes you have running.

Also, do the following;

Repairing the Hard Drive and Permissions

Boot from your OS X Installer disc. After the installer loads select your language and click on the Continue button. When the menu bar appears select Disk Utility from the Installer menu (Utilities menu for Tiger and Leopard.) After DU loads select your hard drive entry (mfgr.'s ID and drive size) from the the left side list. In the DU status area you will see an entry for the S.M.A.R.T. status of the hard drive. If it does not say "Verified" then the hard drive is failing or failed. (SMART status is not reported on external Firewire or USB drives.) If the drive is "Verified" then select your OS X volume from the list on the left (sub-entry below the drive entry,) click on the First Aid tab, then click on the Repair Disk button. If DU reports any errors that have been fixed, then re-run Repair Disk until no errors are reported. If no errors are reported click on the Repair Permissions button. Wait until the operation completes, then quit DU and return to the installer. Now restart normally.

If DU reports errors it cannot fix, then you will need Disk Warrior and/or Tech Tool Pro to repair the drive. If you don't have either of them or if neither of them can fix the drive, then you will need to reformat the drive and reinstall OS X.

Download a utility such as TinkerTool System or Snow Leopard Cache Cleaner and remove all user, system, and font caches (you must restart afterward.)

What you describe is the result of something amiss on your computer that is causing disk space to be used. Only you can discover what that is since you are the one sitting in front of it.

I am also seeing this.

In my case, there seems to be increased swap disk activity.
Open the terminal, cd to /var/vm, and do a ls -l
Every time you see a drop in available space via the Finder, check to see if a new swap file has appeared.

When you restart, the swap files are removed...until something creates them again

If you are using a backup application, check for ghost clones in the /volumes folder.

From the "Finder" Go menu select 'go to folder...' and enter /volumes. Look for any large file with a name that resembles your target backup disk. It's from a failed backup and you can delete it.

Help needed!!

I am having a similar problem. the available space is decreasing automatically on its own and nothing is running..
I lost around 80GB in 20 hours in the available space info.
If I restart the computer, it will be back to normal and start decreasing again slowly on it's own.

Had monitored file size, folder size intensively , no big difference found.
But the available space just keep getting smaller and smaller, it's like an invisible file eating up free space on the hard drive.

Wondering if you ever figure out what's the reason.

some additional suggestions:
- check your trash
- check hard drive for previous system folders
- check idisk (if being used with .mac or .me account) is not loading the backup to your internal drive
- use activity monitor (applications/utilities folder) to view what processes are running (can select % CPU to sort percentage)
- test without internet connection
- select folders within user, get info (command+I) and check totals
- if cannot find lost space, not other disk utility program indicating space, then best is to back up data and erase.

It might be a swap file problem combined with a memory leak. Perhaps a background process is misbehaving. You should shut down all processes that start on login, one by one until you narrow down the culprit.

I recently had this problem -- big time! I noticed that the 500-Gb drive on my MacBookPro 17-inch running Mac OSX (10.6.4) showed only 82 Gb free-space. As I watched, it kept dropping, like watching the gas gauge on your car drop towards empty. I ran Activity Monitor and saw a lot of almost continuous writing activity (20-30 Mb/sec). At first I suspected a virus (madly replicating on my drive), but Norton Anti-Virus detected nothing. I then ran GrandPerspective (freeware that pictorially shows file sizes), and much to my surprise and horror, it looked like way more than half my hard-drive space was occupied by .vbt files from iAntiVirus.

iAntiVirus was something I installed long ago when I was having trouble getting Norton AntiVirus to install properly in OS X 10.6.4. The .vbt files are supposedly temporary files (found in Library/iAntiVirus/temp/xxxxx.vbt) that iAntiVirus creates during scanning operations. These .vbt files contain strings of code from scanned files, and should be auto-deleted upon start-up. Obviously, they were not. Uninstalling iAntiVirus removed an incredible 267,000 files, freeing 284 Gbytes of space on my drive! Wow!

That's exactly what I found. There was a 260GB directory with the name of the backup drive. I use SuperDuper and maybe something happened there.

I will delete this directory and see what happens.