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How much data deletion is enough?

We all know that deleting a file doesn’t actually “delete” anything. Deletion only marks the file’s clusters as free for re-use — data actually remains tucked away within the sectors of each cluster until they are overwritten by new data. To really destroy data, it must be overwritten multiple times. This ensures that the magnetic traces of previous recordings cannot be read with advanced laboratory equipment (even when new data is on the media).

But how many times do you really have to overwrite that deleted data before it’s actually considered secure? Once? Twice? Ten times? Experts say that multiple overwrites are worthwhile — even required — noting that anywhere from 7 to 11 writing passes may be needed to fully overwrite the old data.

And there’s no shortage of tools that promise to kill your old data. Professional products like FDRERASE/OPEN from Innovation Data Processing can securely erase the magnetic disk using three to eight passes. Even end-user products like File Shredder from promise to overwrite file data with random information up to 15 times, claiming that “it is practically impossible to recover the original data”.

Now there are circumstances when it pays to be extra thorough, but personally I think it’s overkill — a practice based on old MFM/RLL drive technologies. US DoD specification 5220.22 calls for three overwrites, while NIST standard SP 800-88 was revised in 2006 to call for only one overwriting pass on modern (post 2001) hard disks.

But I want to hear what you think. What tools are you using? How do you ensure that your old files are securely deleted? Does it even matter to you?

In the mean time, listen to this FAQ on Storage Security where Kevin Beaver offers practical answers to the most common storage security questions he hears from storage pros today.

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Have you hit any roadblocks addressing multichannel scenarios?