How do I erase the free space on macbook pro retina?

Question

I went to erase the free space on my MacBook Pro Retina in the Disk Utility but it says not available for this type of drive. Is there a way I can get around this?

Answer 1

You can't use Disk Utility to securely erase a Solid State Disk drive, because of the fact that SSD's have limited write capability, unlike hard drives, thus have to protect the sectors from as little writes as possible.
In fact TRIM (wear leveling) is enabled to write new data to the least used sectors on a SSD each time.
The NSA guidelines for secure data destruction on SSD's is to grind them into a fine powder.
If you don't require this level of data destruction, you can do this trick below, but not often or you'll premaurely wear out your SSD.
Finder > Duplicate a small file repeatly in a folder until slightly more than 50% of the remaining free space on the SSD is used up, (use Activity Monitor) then delete this folder.
Then duplicate a different small file repeatly in another folder in the same manner.
What this will do is, because of the small file, OS X will fill the smallest unused spots on the SSD, the duplicates will fill the remaining free space half way, then the second folder will (because of TRIM) fill the other remaining 50% of the free space.
You can't fill your boot drive or the machine can refuse to function or boot, but because of the wear leveling this should overwrite all your available free space on the SSD once.
If you have a laptop and TimeMachine, there is a hidden database on the boot drive which will store a copy of the deleted data.
Then there is "versions" and it's possible a copy of the deleted data is stored in that cache file still on the SSD.
I can advise how to delete the TimeMachine backup file on the boot drive, but not the "versions" database or what it contains.
How do I securely delete data from the machine?
If your really paranoid it's likely best to reformat the entire MacintoshHD partition from recovery and then with a new user, then do the Finder > Duplicate procedure to overwrite the deleted data off the SSD, this way the "versions" and TimeMachine databases are also overwritten.
Nothing is safe anymore.