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Date:      Sat, 21 Nov 2009 01:52:30 +0100
From:      Polytropon <freebsd@edvax.de>
To:        "Ronald F. Guilmette" <rfg@tristatelogic.com>
Cc:        freebsd-questions@freebsd.org
Subject:   Re: BTX Loader crashes -- Help wanted
Message-ID:  <20091121015230.cf2c15dd.freebsd@edvax.de>
In-Reply-To: <7972.1258760914@tristatelogic.com>
References:  <7872.1258759936@tristatelogic.com> <7972.1258760914@tristatelogic.com>

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On Fri, 20 Nov 2009 15:48:34 -0800, "Ronald F. Guilmette" <rfg@tristatelogic.com> wrote:
> But I have one question.  The author sez to do this:
> 
>    dd if=8.0-BETA1-amd64-memstick.img of=/dev/da0 bs=10240 conv=sync
> 
> I just want to know what the effect of conv=sync and why it might be
> necessary.

According to "man dd":

     bs=n     Set both input and output block size to n bytes, superseding the
              ibs and obs operands.  If no conversion values other than
              noerror, notrunc or sync are specified, then each input block is
              copied to the output as a single block without any aggregation
              of short blocks.

in conjunction with

     conv=value[,value ...]
              Where value is one of the symbols from the following list.

              sync     Pad every input block to the input buffer size.  Spaces
                       are used for pad bytes if a block oriented conversion
                       value is specified, otherwise NUL bytes are used.

it appears that the data is ensured to be "properly
aligned" with a possibly different block size on the
source or target media. As far as I remember, not
giving the bs= argument would result in a default
block size of 512 bytes which may - but don't ask
me why - lead to a non-functioning target USB stick.




-- 
Polytropon
Magdeburg, Germany
Happy FreeBSD user since 4.0
Andra moi ennepe, Mousa, ...



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