On Wednesday 02 September 2009 22:39:24 you wrote: > On 02Sep2009 22:17, Marko Vojinovic <vvmarko@xxxxxxxxx> wrote: > | On Wednesday 02 September 2009 21:32:32 Dean S. Messing wrote: > | > I have a terebyte sata drive that I need to securely wipe clean. > | > | I have always wondered about this, why not just do a rm -rf * on the > | drive, then put one big file on it (some divx movie or such), and copy it > | over and over under different names until the drive space gets exhausted > | completely? This can easily be scripted, and I believe it would work as > | fast as possible for a drive of given capacity. > > Copying /dev/zero is a fast way to get an arbitrary amount of data (my > standard anecdote involves emptying it, which I did once on an ancient > system). It will be faster than copying a real file since the "read" > part is free. You are right, zeroing is faster of course. I mentioned a dvix movie just to make the data written more random than all-zeroes, which might be more secure, but the end result is the same, I guess. :-) > HOWEVER: > > The purpose of shred is to rewrite the data many times with random data, > since it is technically possibly to read "old" patterns from the drive > with the right (expensive and special) hardware. This is the part that puzzles me. Let's give it a following thought experiment. Suppose I have all that state-of-the-art expensive and special equipment at my disposal, and unlimited free time. So I fill the drive with data1, zero it out, fill it with data2. Are you saying that I can use the equipment to recover the old layer of data1 (all or some part of it)? Then I could zero the drive again, fill it with data3. Can I use the equipment to recover both data1 and data2 layers which have been deleted? Suppose I repeat the process arbitrarily many times. At some point data1 layer would have to be lost completely, since otherwise it would mean that there is a way to read and write infinite amount of data on the drive, which is impossible. So the question is: if you suppose I have in my possession a yet-to-be- invented-most-expensive-CIA-NSA-dream-about-it-machine for data recovery, how many times should a typical drive be zeroed over and over in order to destroy that first layer of sensitive data beyond any chance of recovery, even in principle? Given that I know so little about modern hard drives, I can only guess, but I guess the number of such rewrite-cycles is ridiculously small, like 3 or maybe 4 top. It would need a serious scientific study to convince me that it needs 5 times to do it. So what's all the fuss and hype about deleting drives, then? Create a script to zero out (or random out) the drive four times, let it run for a week, and be done with it. There should be some extremely serious arguments to convince me that this would not be completely effective on any drive. Best, :-) Marko -- fedora-list mailing list fedora-list@xxxxxxxxxx To unsubscribe: https://www.redhat.com/mailman/listinfo/fedora-list Guidelines: http://fedoraproject.org/wiki/Communicate/MailingListGuidelines
