shredding files on a flash drive

[Lennart Sorensen]

On Fri, Jan 18, 2008 at 03:09:15PM -0800, Kristian Erik Hermansen wrote:
> On Jan 18, 2008 2:22 PM, Lennart Sorensen <lsorense-1wCw9BSqJbv44Nm34jS7GywD8/FfD2ys at public.gmane.org> wrote:
> > The file system has no clue and no say in how things are done under the
> > hood by a flash based device.  Blocks get remapped all the time as part
> > of wear leveling and hence spare blocks are rotated into use when other
> > blocks are overwritten.
> 
> So are you saying that the secure overwrite will not happen?  Well,
> then dd if=/dev/zero of=/dev/sda sounds like a good option then :-)

Writing 0xFF is preferable to avoid unnecesary wear (and should be
faster too if the flash controller has some brains which it probably
doesn't).

And the dd still only works assuming all spare blocks are always erased
when they become free, which for performance reasons would be the right
thing to do (that way the blocks are ready for writes when needed rather
than having to wait for an erase before write later on).  But you have
no way to know for sure how the flash controller does things.

--
Len Sorensen
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