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When installing a new AIX server, there is a possibility to use several patterns for secure deletion.

My question: Is it necessary to use several patterns? What is the benefit from having several ones?

marked as duplicate by Rоry McCune, TildalWave, Adi, Polynomial, dr jimbob Jan 23 '14 at 15:54

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  • Now after his edit, I agree with the OP. This isn't a dupe. This is essentially asking "With one pass, is the pattern 00 better than the pattern ff?" Or "Are all overwriting pattern the same?" – Adi Jan 23 '14 at 16:32
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No, it isn't necessary.

With modern (less than 10 year old) hard drives, it is not required to overwrite a disk more than once.

There is an often cited paper which says that you need to overwrite data at least 10 times to be sure, but that paper is over 20 years old and thus applies to outdated hard drives. Modern hard drives use much weaker magnetic fields and much more sensitive read-heads to reach higher data densities. As a result their data is a lot less persistent.

This has been proven in the paper "Overwriting Hard Drive Data: The Great Wiping Controversy" by Craig Wright and Dave Kleiman from 2008.

You might wonder: "Then why is there still software which offers to overwrite hard disks dozens of times with all kinds of sophisticated patterns?" The answer is that people are paranoid when it comes to security. When they heard somewhere that a hard drive can be restored after a single pass, even when the source is dubious, they won't trust a software product which doesn't do it. Also, there are some outdated standards for IT security around which still have that myth and which must be followed by some organizations, even when they know that it's snake oil.

  • I wasn't aware of this. Good to know =) – kiBytes Jan 23 '14 at 15:28
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    To be clear, disks bigger than 15GB manufactured after 2001 will not be vulnerable to MFM analysis after a single wipe pass. Older and smaller disks may be, so you should use the DoD spec overwrite procedure if you want to be secure against state-level threats. Note that MFM technology isn't exactly something your average hobbyist keeps in his shed. – Polynomial Jan 23 '14 at 15:50
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They are necessary, using several patterns is needed to ensure secure deletion.

When doing secure deletion of a disk (and we are not toking about SSD here), you must ensure that your bits changes their position several times so that it is impossible even with finest hardware to guess what has been stored before the current information (residual magnetic fields).

That is the same mechanism "secure deletion utilities" work, but they usually use several passes with random data.

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    This is theoretically potentially true historically, but certainly not true in practice today. – Xander Jan 23 '14 at 15:26
  • Shame on me... I wasn't aware this is only for old disks... I will update my sources regarding this topic. :( – kiBytes Jan 23 '14 at 15:27

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