> This is just plain wrong. For modern hard drives (manufactured after > 1994), it is sufficient to overwrite the disk once, with any pattern you > desire. I'm not talking about floppy diskettes or core memory here, I'm No it is not, because of things like block sparing. > talking about hard disks. > Also, I would bet that the longer the data had not been re-written, the > less embeeded it is, not more embedded. Again, we're not talking about > core memory. > Google "Advisory No. LAA-006-2004" for NSA's statement on this. http://www.dtic.mil/whs/directives/corres/pdf/522022mchaps.pdf is a process manual. It's not precisely defining such things. It's also a very boring manual but happy reading. > and some of the old hard disks, like the RM03s. But for modern hard > drives, a single overwrite pass makes it impossible to recover prior data > from that particular location. That is they key bit.. the drive is not in any way required to re-use the same locations for the data. Furthermore a drive is perfectly entitled to optimise some types of common access (eg it could remember zeroed blocks by list). For rotating media sparing and some other goings on actually mean you won't always hit the same block. Move from simple rotating media and it all gets much more complex with SSD, flash caches and the like. Whether it matters really depends upon how valuable the data is and who the bad guys are. You at the very least talking a recovery tools and custom firmware. A lot of the people who can do that can also turn up at your front door with a warrant and ask you politely for the information anyway. Because of all this the ATA standards define a secure erase command which instructions the drive to securely erase its contents. On most rotating media this does a data erase of all data sectors in a way the drive itself knows is ok. On flash it may be handled various ways and on a lot of flash drives it is *much* faster than blanking all the sectors (almost instantaneous in fact), at least as secure as blanking all the sectors and doesn't cause drive wear in the same way. If you want to erase your drive, issue a secure erase command. It's as simple as that. If you aren't fussed just overwrite the metadata, but that in itself doesn't make old files that hard to recover, at least on VFAT file systems. Alan -- users mailing list users@xxxxxxxxxxxxxxxxxxxxxxx To unsubscribe or change subscription options: https://admin.fedoraproject.org/mailman/listinfo/users Guidelines: http://fedoraproject.org/wiki/Mailing_list_guidelines
