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[Bug-ddrescue] How about a "don't care" block state?

From: Ian Abbott
Subject: [Bug-ddrescue] How about a "don't care" block state?
Date: Wed, 18 May 2011 16:28:34 +0100
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Hi folks,

Would it be useful to have an explicit "don't care" block type in the
log file?  ddrescue wouldn't bother to read these blocks from the source
or write them to the destination.  (However, in '--direct' mode, it
might need to read parts of the "don't care" blocks due to alignment
restrictions on the block device.)

My idea is that it should be fairly easy to modify a utility such as
'partclone' (actually, a suite of utilities for cloning various file
systems) to spit out a ddrescue log file.  If it spat out a '?' for the
used areas of the file system and a 'X' (or whatever will mean "don't
care") for the unused areas, this log file could be used by ddrescue to
recover only the used areas of the file system, ignoring the unused areas.

The same thing could be achieved without an explicit "don't care" block
type; the utility creating the log file could spit out a '+' for the
unused blocks to pretend they have already been copied by ddrescue.
However, a separate block type seems preferable both to avoid confusion
and so that "good" blocks can be distinguished from "don't care" blocks
when ddrescue is running in '--fill' mode.

Thanks to Antonio and everyone else who have worked on ddrescue.  I've
used it many times!


-=( Ian Abbott @ MEV Ltd.    E-mail: <address@hidden>        )=-
-=( Tel: +44 (0)161 477 1898   FAX: +44 (0)161 718 3587         )=-

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