Macbook Pro storage filled completely by other

Question

I've been getting the message that my Start Up Disk Is Full. So I went to About This Mac > More Info > Storage and noticed the following:
How is the possible I know I only have about 200GB of information on this computer?
How do I fix this?
Im running Mac OS X Lion software.

Answer 1

“Other” Storage
A commonly asked question is what is included in the "Other” storage category reported in the About This Mac Storage display.  Other includes everything that is not audio, movies, photos, apps and backups.  In other words it includes the OS, mail, documents...  See http://pondini.org/OSX/LionStorage.html and What is "Other" and What Can I Do About It? and Apple Support Communities https://discussions.apple.com/docs/DOC-5142
Recovering Disk Space
If you have less than 10 GB you definitely need to delete or offload some files or purchase a lager disk or SSD (see below).  You may want to maintain at least 20 GB of free space so when your disk starts filling again it will have some room before it hits that 10 GB mark again.  More headroom is better.  If you let the space fall much below 9 GB you might not be able to boot your machine.
Initial easy steps to gain disk space:
- Delete all files in the Downloads folder.
  Empty the Trash.
- Start iPhoto.
  Empty its trash.
  Restart.
- Restart in Safe Mode:
  Restart the computer.
  As soon as you hear the chime press and hold down the right shift key.
  Be patient. Hold it down until you see the Apple icon.
  Empty the trash.
  Restart in normal mode.
- Delete "Recovered Messages", if any.
    Hold the option key down and click "Go" menu in the Finder menu bar.
    Select "Library" from the drop down menu.
    Library > Mail > V2 > Mailboxes
    Delete "Recovered Messages", if any.
- Empty the Trash.
- Restart.
- Re-index your system disk (Macintosh HD):
  http://support.apple.com/kb/ht2409
Backup:
Run a Time Machine (or other) backup since you are about to delete and move files and you may need to recover from any inadvertent mistakes or decisions.  You will need one external hard drive for your Time Machine (or other) backup and a second if you plan to offload some files.  (See suggestions for where to purchase hard drives at the end of this message.)
For more about backups:
Time Machine Basics: http://support.apple.com/kb/ht1427
Most commonly used backup methods:
https://discussions.apple.com/docs/DOC-3045
Methodology to protect your data.  Backups vs. Archives.  Long-term data protection:
https://discussions.apple.com/docs/DOC-6031
Deleting files:
Then use the free application OmniDiskSweeper http://www.omnigroup.com/more to explore your volume in descending order by size so you can attack the problem from the top down, deleting the largest unwanted files first.  Delete with caution and do not delete any system files.  Do not rely on restoring files from Time Machine; delete only those files you never want to see again.  Remember to empty the trash after trashing the files.
Additional references on freeing disk space:
http://pondini.org/OSX/DiskSpace.html
http://www.macmaps.com/diskfull.html
Offloading files:
Consider moving some of the no-often-used large files or directories to an external disk.  Use ODS again to find them.  As noted above this will be at least your second hard drive.  Your first one(s) is/are for your Time Machine (or other) backup(s).  Do not offload files onto a Time Machine disk.
Format the second drive as Mac OS Extended (journaled).  Using OWS to find large files/folders and copy them from the system drive to the external hard drive and delete them from your internal drive.
Then  > System Preferences > Time Machine > Options… > Remove the offload HD name from the exclusions list.
Now both your system disk and your external offload disk will be backed up onto your Time Machine disk.
From: http://www.thexlab.com/faqs/freeingspace.html
To move your iTunes Music folder to another disk or partition:
To change the location of your iTunes Music folder, carefully follow the instructions in the AppleCare® Knowledge Base document "iTunes for Mac: Moving your iTunes Music folder."Additional information can be found in iTunes Help.
http://webcache.googleusercontent.com/search?q=cache:http://www.thexlab.com/105/ 00000849.html
Laptop users may want to consider having two iTunes libraries: a small library of current favorites on their computer, while their complete library resides on an external hard drive. Utilities like iTunes Library Manager enable you to easily have multiple iTunes libraries you can use with your account.  https://www.macupdate.com/app/mac/7689/itunes-library-manager
To move your iPhoto Library folder to another disk or partition:
To move the iPhoto Library folder to a new location, employ the instructions in the AppleCare Knowledge Base document from http://support.apple.com/kb/PH2506 corresponding to the version of iPhoto you are using. Additional information can be found in iPhoto Help.
Laptop users may want to consider having two iPhoto libraries: a small library of current, favorite photographs on their computer, while their complete library, or archives of older photos are saved on an external hard drive. Utilities such as iPhoto Buddy and iPhoto Library Manager enable you to have multiple iPhoto libraries that you can use with your account.
https://www.macupdate.com/app/mac/12175/iphoto-buddy
https://www.macupdate.com/app/mac/7158/iphoto-library-manager
Hardware — Bigger disk/SSD:
If your system has upgradeable storage then if you are still tight on disk space consider larger storage.  If you have a disk consider replacing it with a one TB disk.  Check out an upgrade to an SSD-Hybrid disk. Google "Seagate 1TB Solid State Hybrid Drive SATA 6Gbps 64MB Cache 2.5-Inch".  If you have an SSD consider increasing its capacity to 240 or 480 GB.  A standard 240 GB SSD would cost from $200 to $280. See OWC and Crucial: http://www.crucial.com/ for options.  OWC sells 120, 240 and 480 GB SSD upgrades for MacBook Airs.  A 240 GB upgrade costs $265.   http://eshop.macsales.com/shop/SSD/OWC/ .  If your Mac is under warranty or AppleCare replacing the SSD will void the warranty.
For backups and offloading data to an external drive, PlotinusVeritas gives some great suggestions for purchasing external hard drives in this thread:
https://discussions.apple.com/thread/5602141?tstart=0