Re: [gentoo-user] Want to seriously test a NEW hard drive

[William Kenworthy <billk@iinet.net.au>]

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