[CentOS] Utility to zero unused blocks on disk

Tue Feb 9 06:18:37 UTC 2016
John R Pierce <pierce at hogranch.com>

On 2/8/2016 9:54 PM, Chris Murphy wrote:
> Secure erase is really the only thing to use on SSDs. Writing a pile
> of zeros just increases wear (minor negative) but also doesn't
> actually set the cells to the state required to accept a new write, so
> you've just added a lot more work for the SSD's garbage collector and
> wear leveling, so it's going to be slower than before you did the
> zeroing. Secure erase on an SSD erases the cells so they're ready to
> accept writes.

at least one SSD I had, the vendor told me writing a full pass of zeros 
on it via dd or whatever would completely reset the garbage collection 
and effectively defrag it.

john r pierce, recycling bits in santa cruz