||11-05-2012 06:04 AM
Anything better than 1 pass should be ok. The 35-pass scheme is a misinterpretation of Gutmann's 1996 paper.
Gutmann, Peter. (July 22–25, 1996) Secure Deletion of Data from Magnetic and Solid-State Memory. University of Auckland Department of Computer Science. Epilogue section. (writing, "In fact performing the full 35-pass overwrite is pointless for any drive since it targets a blend of scenarios involving all types of (normally-used) encoding technology, which covers everything back to 30+-year-old MFM methods (if you don't understand that statement, re-read the paper). If you're using a drive which uses encoding technology X, you only need to perform the passes specific to X, and you never need to perform all 35 passes. For any modern PRML/EPRML drive, a few passes of random scrubbing is the best you can do. As the paper says, "A good scrubbing with random data will do about as well as can be expected". This was true in 1996, and is still true now."). http://en.wikipedia.org/wiki/Gutmann_method