Re: Adding of peter gutmann's paper concept to /bin/rm

Dirk-Willem van Gulik <dirkx@webweaving.org> writes:
> On Wed, 26 Mar 2003, Ted Unangst wrote:

Well, that's a nice theory. But I don't think they make MFM drives anymore. Modern drives generally provide a sort of "virtual" interface to the actual physical drive, which may actually work considerably different than the interface might suggest. For instance, the number of heads, cylinders, & sectors is very likely to be way different, and the number of sectors per track may vary between the inside & outside of the disk.

But there's a way worse problem than this. Many modern drives at least support some form of hardware bad blocking. This could happen at any time, and if it does, the "bad" block may contain recoverable data. It's also quite common to support some sort of buffering - that means the interface layer reads and writes don't necessarily translate directly into hardware reads and writes. It's perfectly possible that the drive might perform some sort of write compression (deleting "redundant" writes to the same spot on the disk), and it might also leave data in the buffer that isn't written to disk. That buffer may even be stored in nvram. Even ordinary cheap laptop disks may have all of these characteristics, but most forms of hardware RAID, especially the higher levels, are guaranteed to have these features in spades.

                                -Marcus Watts Received on Fri Mar 28 17:03:45 2003