From: jdbeard@patriot.net   
      
   On 04/20/2013 10:50 AM, Daniel47@teranews.com wrote:   
   > Jim Beard wrote:   
   >> On 04/19/2013 09:11 AM, Daniel47@teranews.com wrote:   
   >>> Wolfgang Schelongowski wrote:   
   >>>> "Daniel47@teranews.com"  writes:   
   >>>>   
   >>>> [saving a 'broken' partition/disk]   
   >>>>   
   >>>>> Now, just in case the HD is dying, I'd better dd this drive to   
   >>>>> my spare,   
   >>>>> as suggested by others.   
   >>>>   
   >>>> You want to use dd_rescue instead of dd AND send all its   
   >>>> (error-)messages into a file. RTFM of dd_rescue first, of   
   >>>> course.   
   >>>   
   >>> Wolfgang, firstly, I have my Home (sda8) up and running again, so   
   >>> do I really need dd_rescue?? I was just meaning to use the dd   
   >>> command to copy my sda drive to a spare (sdb) drive, as a   
   >>> back-up.   
   >>>   
   >>> I tried man dd_rescue but was told "No manual entry for   
   >>> dd_rescue".   
   >>   
   >> As mentioned elsewhere, there seem to be three versions of dd   
   >> rescue,   
   >> and whichever you use you will have to install it.  It is not   
   >> installed   
   >> by default, but is available in the Mandriva repositories.   
   >>   
   >> The problem with dd is that it chokes when it encounters bad   
   >> sectors.   
   >> The dd rescue versions deal with such problems, with what each   
   >> will do   
   >> in specific circumstances differing.   
   >>   
   >> Cheers!   
   >>   
   >> jim b.   
   >   
   > O.K., Jim, thanks for that.   
   >   
   > I thought that the dd command didn't care if the sector was   
   > occupied or not, or good/bad/indifferent, it just copied the   
   > sector, whatever it was!   
      
   A sector that cannot be read cannot be copied.  Literally.  It   
   can be replaced with a sector of 0s, or it can be ignored, or a   
   stream of random bits can be provided in its place, but it cannot   
   be copied.   
      
   For this and certain other conditions, dd will fail, by design.   
      
   When the sector that cannot be read contains inodes (data on what   
   files exist where within the file system), there are a variety of   
   things that can be done to recover some of the information.   
   Search for information on the various versions, or read the   
   source code if you really want to know what these programs will do..   
      
   Cheers!   
      
   jim b.   
      
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