Date: Sun, 8 Jul 2007 11:11:36 -0700 (PDT) From: Michael Eubanks <mse0206@yahoo.com> To: freebsd-chat@freebsd.org Subject: Re: compressed HDD image using dd...clearing unused blocks Message-ID: <452829.7742.qm@web58108.mail.re3.yahoo.com> In-Reply-To: <20070708112413.GA27077@psconsult.nl>
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--- Paul Schenkeveld <fb-chat@psconsult.nl> wrote:
> On Sat, Jul 07, 2007 at 10:28:01PM -0700, 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.
>
> What about:
>
> # dd < /dev/zero > BIG_EMPTY_FILE bs=128k
> # rm BIG_EMPTY_FILE
>
> Comes close to what you want, only a couple of
> indirect blocks are
> not zeroed this way but the majority of unused
> blocks will be.
>
...snip...
I'll give it a shot. That is a great idea. I'm
wondering, though, what happens when the filesystem is
filled? In the past, the system became unstable when
the filesystem was full. I'm guessing that's why a
blocksize of 128k bytes was used - all blocks but the
last (<128k) will be filled? Is that a correct
assumption? What if I just bumped that number up to
4m or something to speed things up?
-Michael S. Eubanks
mse0206@yahoo.com
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