Data Destruction

How many times should a hard drive be overwritten before one can safely assume its data is no longer retrievable?

A lot of shady software vendors tell you that you should overwrite repeatedly with various patterns, such as the 35-pass method created by Peter Gutmann more than 30 years ago. Some of these packages are free, most of them cost some arbitrary amount of money. All of them are a waste of money.

Even Mr. Gutmann stated that any hard drives that came out after the early 90's MFM and RLL drives can simply be overwritten once with random data. Sticking a decommissioned hard drive into any unix-like box, or booting the system with a live-CD version of Linux, and simply overwriting it with "dd if=/dev/urandom of=/dev/" will do the trick, and it won't cost you anything.