That's some serious wiping you're doing. I suspect that it must take a fierce amount of time to complete. An alternative approach would be to securely wipe the contents of sensitive files before deleting them. This will be much, much faster. Also, from the way I read it, you might scribble garbage on a large section of the free space of the disk and still manage to avoid overwriting an area where sensitive information lies waiting to be recovered.
The US Department of Defense lays down guidelines for deleting files in what's known as the Orange Book. descartes wrote Shred to do just that.
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