Replacing Drive with SSD

Matthew Seaman m.seaman at
Fri Aug 28 09:14:32 UTC 2015

On 08/28/15 09:46, Matt Smith wrote:
> I've heard a rumour that you should never use dd with SSD drives because
> of the wear levelling stuff. Apparently SSDs automatically make sure
> that data is sent to unused flash cells so that all the cells wear
> evenly, but if you use dd on them it makes them think that every single
> cell is in use which screws this up?

Hmmm.... Yes, dd will copy all of the source disk including disk blocks
that are unused, empty space.  Overwriting a cell that is already zeroes
with yet more zeroes is a waste of time, but I don't know if that would
actually use up some of the life of that cell.  It shouldn't confuse the
wear-levelling code on the drive particularly -- it might take a little
while to sort itself out after the fact, but it's no worse conceptually
than filling the drive up with a big file and then deleting that file.

So, avoid using dd if you can, but it's probably not a disaster if you
can't avoid it.



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