compressed HDD image using dd...clearing unused blocks
Darren Pilgrim
freebsd at bitfreak.org
Sun Jul 8 17:58:01 UTC 2007
Michael Eubanks wrote:
> Hello all,
>
> I am updating a system that has been around for some
> time now. I would like to make a compressed disk
> image after the final setup is complete, although, I'm
> guessing that the unused blocks will not allow me to
> compress the image as well as I could with a
> previously clean disk (considering the disk has been
> in use for some time now). Is there a way to do this
> - zero out unused blocks to optimize compression? I
> generally do this with Windows machines using the
> cipher command (killing cipher after it has finished
> writing zeroes). After running cipher I use dd to
> create a compressed HDD image for later use. I'd like
> to be able to do the same with FreeBSD.
In my experience, using dd to create images of UFS/UFS2 volumes is
problematic, though I can't qualify that. It's better to use an
archival program like dump or tar, IMO. That approach also gets you a
restored volume with no fragmentation.
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