(Sorry for the late reply, I hope it's still useful to you.) On Dienstag, 4. April 2017 00:46:54 CEST Kai Krakow wrote: > Am Mon, 3 Apr 2017 16:15:24 -0400 > > schrieb Rich Freeman <ri...@gentoo.org>: > > On Mon, Apr 3, 2017 at 2:34 PM, Kai Krakow <hurikha...@gmail.com> > > > > wrote: > > > Just dd /dev/zero to the complete device. That purges everything you > > > need: partition tables, boot sectors, contents: > > > > > > # dd if=/dev/zero of=/dev/sdX > > > > If it contains data you'd prefer not be recoverable you might want to > > use shred or ATA secure erase. > > I wonder if shredding adds any value with the high density of modern > drives... Each bit is down to a "few" (*) atoms. It should be pretty > difficult, if not impossible, to infer the previous data from it. I > think most of the ability to infer the previous data comes from > magnetic leakage from the written bit to the neighbor bits. And this is > why clever mathematicians created series of alternating bit patterns to > distribute this leakage evenly, which is the different algorithms the > shredder programs use. > > Do you have any insights on that matter? Just curious.
For the record, there was some discussion on this on this not too long ago [edit: oops, looks like it was almost two years ago now]: see the thread "Securely Securely deletion of an HDD" (yes, I including my spelling mistake), which you can find online at https:// archives.gentoo.org/gentoo-user/message/a01e0ad7b07855647a528f1e0324631a and https://archives.gentoo.org/gentoo-user/message/582fe3c66c7e13de979b656e9db33325. > > Shred overwrites the drive with random data using a few passes to make > > recovery more difficult. Some debate whether it actually adds value. > > For a mere mortal it is already impossible to recover data after > writing zeros to it. Shredding is very time consuming and probably not > worth the effort if you just want a blank drive and have no critical or > security relevant data on it, i.e. you used it for testing. > > But while you are at it: Shredding tools should usually do a read check > to compare that the data that ought to have been written actually was > written, otherwise the whole procedure is pretty pointless. As a side > effect, this exposes sector defects. > > If you want to do this to pretend data has never been written to the > drive, you're probably out of luck anyways: If you'd be able to recover > data after a single write of zeros, it should be easily possible to see > that the data was shredded with different bit patterns. The S.M.A.R.T > counters will add the rest and tell you the power-on hours, maybe even > amount of data written, head moves etc. > > (*): On an atomic scale, that's still 1 million atoms... I don't think using zeros is enough, certainly not on SSDs that do their own compression, I would think. And AFAIK using random data can still fill the drive at native write speed, so I don't see what you gain by avoiding that. But really, if you haven't already, check the primary sources in the thread I mentioned above. HTH -- Marc Joliet -- "People who think they know everything really annoy those of us who know we don't" - Bjarne Stroustrup
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