[CentOS] Utility to zero unused blocks on disk

Tue Feb 9 05:22:11 UTC 2016
Chris Adams <linux at cmadams.net>

Once upon a time, Robert Nichols <rnicholsNOSPAM at comcast.net> said:
> On 02/08/2016 07:04 PM, Chris Adams wrote:
> >For that purpose, use something that can TRIM a VM image, like
> >virt-sparsify.
> That's doing the same thing.
> virt-sparsify works by mounting the filesystem, filling it to capacity
> with zeros, then performing a copy operation which skips over the
> all-zero blocks, leaving them unallocated in the sparse destination
> file.

Well, that's the slow method that copies the image.  There's also the
in-place method, which just does a TRIM that pokes holes in the original
image (much faster and uses no extra disk space).

Chris Adams <linux at cmadams.net>