From owner-freebsd-hackers  Tue Jul 13  5:57:44 1999
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From: Luigi Rizzo <luigi@iet.unipi.it>
Message-Id: <199907131250.OAA00397@prova.iet.unipi.it>
Subject: Why 'dd' does not seek over 'char' devs (specifically raw disk partitions).
To: hackers@freebsd.org
Date: Tue, 13 Jul 1999 14:50:34 +0200 (CEST)
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Hi, i have a question.

Why 'dd' does not seek over 'char' devs (specifically raw disk partitions).

My point is, when a disk develops problems, sometimes it is possible
to recover nearby sectors e.g. using dd, and seeking to the right
block. However running dd over the char device (rwd*) takes forever
because the seek on char devices is implemented by reading instead.
Using the cooked device is problematic because the buffering causes
multiple sectors to be read and this may cause errors if some block
nearby has problems.

I notice that on output lseek _is_ used also on char devices.

Ideas ?

	cheers
	luigi


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