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Date: Tue, 27 Dec 2016 20:48:27 +0100
From: Polytropon <freebsd@edvax.de>
To: galtsev@kicp.uchicago.edu
Cc: freebsd-questions@freebsd.org
Subject: Re: Fwd: dd -bs=BYTES  read and write up to BYTES at a time   
 system -invalid  number 1m   #### dd 
 if=FreeBSD-11-RELEASE-amd64-memstick.img of=/dev/sdb1 bs=1M   conv=sync
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On Tue, 27 Dec 2016 13:32:09 -0600 (CST), Valeri Galtsev wrote:
> The vital where you _should_ use "bs=2048" is when you dump a track of
> CD/DVD.

Except when you are dealing with _audio_ CDs, then you
need bs=2352 for raw data. :-)



> (especially when doing recovery of badly damaged CD, then few
> extra options are a must to make exact sector for sector copy or bit for
> bit, even though in some unreadable areas they are are filled with
> zeroes).

Tools like dd_rescue can dynamically adjust the block size
and re-read with decreasing sizes (and even repeat several
times) in case of read errors.




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