On Wed, 2012-08-08 at 14:02 +1000, Adam Carter wrote: > > I have seen where people use dd to do this sort of thing to. I read > > somewhere that if you do a dd and put in all 1's, then all 0's then back > > again that it is very hard to get any data back off the drive. I think > > if you do it like over a dozen times, it is deemed impossible to get > > anything back. I think that is the Government standard of it's gone. > > I've heard the old attacks to recover data from a zerod drive are no > longer viable for disks of greater capacity than about 10G. I haven't > seen the information myself, however. > > A single pass using dd would probably a good way of detecting any > existing bad blocks, so a smartctl then dd then smartctl again and a > diff of the results may be interesting. > > I just use a 1TB software mirror for my backups. >
To wipe a drive use dban. - live CD which uses (US) gov approved standards of wipe methods/patterns. dd is only going to show sectors on a failed drive - too late! To explain, modern drives have a store of locations they can use to transparently replace any failed locations (apparently similar to the way SSD's do it) - the internal drive electronics handle this and its not visible externally though smart data seems to show it, but as google says, smart is a bit suspect. The problem of a bad sector will only show once all the reserved locations are used up, by which time the drive is usually in rampant failure. I do suspect this is one reason for googles results - actual failures of the media (as against the motors/electronics are much as they always have been, but the drives are not reporting them until its too late. BillK
