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Date: Fri, 29 Sep 2017 08:08:23 +0100
From: Bob Eager <rde@tavi.co.uk>
To: freebsd-fs@freebsd.org
Subject: Re: How to create holes in files ?
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On Fri, 29 Sep 2017 08:26:13 +0200
Ben RUBSON <ben.rubson@gmail.com> wrote:

> Unfortunately here storage blocks will be set/written to 0,
> they will not be freed/recovered, a file hole will not be created.

You need to add:  conv=sparse    to the dd command to turn zero blocks
into unallocated blocks.