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Jeroen W. Pluimers on .NET, C#, Delphi, databases, and personal interests

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SysInternals sdelete: zero wipe free space is called -z instead of -c

Posted by jpluimers on 2016/09/20

In the 2009 past, sdelete used the -c parameter to zero wipe clean a hard drive and -z would clean it with a random pattern.

That has changed. Somewhere along the lines, -c and -z has swapped meaning which I didn’t notice.

This resulted in many of my virtual machines image backups were a lot larger than they needed to be.

The reason is that now:

  • -c does a clean free space with a random DoD conformant pattern (which does not compress well)
  • -z writes zeros in the free space

Incidently, -c is a lot slower than -z as well.

TL;DR: use this command

sdelete -z C:

Where C: is the drive to zero clean the free space.


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