There are Levels 1 through 5. Which level do I use?
All levels erase the disk completely. The only difference is how difficult it would be for someone to recover data from the disk using sophisticated recovery tools (including scanning tunneling electron microscopes). Level 1 is the fastest, level 5 is the slowest. Level 5 is the most secure, level 1 is the least secure. I personally couldn't recover anything from a disk that had been cleaned with level 1, but someone with the know-how and a few thousand dollars could. I'm not guaranteeing anything, but I doubt the NSA could recover anything from a disk that had been cleaned with level 5. Level 3 meets most corporate and nonclassified government erasure specifications. Here's what each level does:
1 - A single pass of all zero.
2 - One pass of random data followed by one pass of all zero.
3 - Three passes: all zero, all one, all zero.
4 - Ten passes, some of which are random, followed by one of
5 – 25 passes, three of which are random.