SUMMARY: Wiping a disk, part II

From: Christopher L. Barnard <>
Date: Wed May 19 2004 - 12:46:28 EDT
I asked

> A followup to my question last week about wiping a disk:
> for those of you using
> dd if=/dev/random of=/dev/rdsk/cXtXdXsX
> how long does it usually take?  On a 2gig disk after it had been running
> for over 24 hours I phoned Sun Support to see if maybe I had gotten the
> flags to dd wrong or something like that.  The woman I spoke to was
> insistent that a repartition and newfs was all that was necessary to
> wipe a disk of all previous data.  Yeah, right.  Sure.  And Microsoft
> will start making a secure and well written product.  So, how long does
> that command usually take?
> TIA, and I will summarize.

Damn, that was fast.

/dev/random has to generate entropy and is very CPU intensive every time
it is called.  Use /dev/urandom if you must (it is orders of magnitude
faster than /dev/random), but /dev/zero (which is orders of magnitude
faster than /dev/urandom) with multiple passes (7 for government specs,
I understand) is much faster and works fine.  Also, tweak the block
size.  bs=1024k seems to be the fastest.

dd if=/dev/zero of=/dev/rdsk/cXtXdXsX bs=1024k
format (to label the disk again)
rinse, lather, and repeat 7 times.

Thanks to the 15 or so people that responded to my query within minutes...

| Christopher L. Barnard         O     When I was a boy I was told that |
|         / \    anybody could become president.  |
| (312) 347-4901               O---O   Now I'm beginning to believe it. |
|                --Clarence Darrow |
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Received on Wed May 19 12:46:24 2004

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