On Mon, 2006-02-06 at 18:12 +0100, Francois Barre wrote: > A couple of years back in time, there were some tools to read and then > rewrite floppy contents to remagnet the floppy content. I guess it > shall be the same for the drive : periodically re-read and re-write > each and every sector of the drive to grant a good magnetation of the > surface. I don't think this applies so much anymore. The coercivity of modern, high-density magnetic media is quite a lot higher than that of floppy disks. These days when you encode it, it really stays unless a very strong magnetic force acts on it. Much stronger than that of any household magnet. That's why waving a big magnet over modern tapes doesn't actually do anything to them (or so I'm told, I still need to test that, but I don't use tape for backup anymore so I don't really have the materials handy). The strength of the magnet is not powerful enough to overcome the coercivity of the media. I don't know about those molybdenum magnets. It's a problem in data remanance protection (ensuring that the data is *really* gone on a hard disk). Just to go OT for a second, doing one of those 32+ pass security wipes won't necessarily protect you against a highly motivated attacker with a scanning tunnelling microscope. This is because the data can be laid down on a track, but the heads can move every so slightly (but still well within tolerances) out of alignment. When you do your 32+ passes, there is still a very small strip of the data left that can be recovered. The US military used to melt their drives into slag, but then EPA regulations put a stop to that because of some of the more exotic chemicals in the drive. Now they apparently use one of their 2.4MW electomagnets for the job. Apparently the platters end up pressed against the top of the drive. :) Neil - To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
