[TriLUG] getting dd if=[flaky device] to ignore read errors

[Brian Henning]

Sweet!  That looks like it's working.  Slowly, of course..  There appear 
to be more bad sectors than I originally thought.  Alas.  In the 12 
hours it's been running, it's averaging around 715 kB/sec.  If that's 
representing the average error rate (and I hope it's really worse than 
the average error rate...), it should only be another 50 short hours 
until it's done!  Maybe I should get a cup of coffee...

To Ian's suggestion of dd_restore, looks like that package only improves 
upon dd with the hard and soft block sizes, and back-to-front transfer. 
  Clever, but not clever enough for me to restart the process over 20 
hours in.

Thanks for the valuable suggestions!

~Brian

Kevin Otte wrote:
> Brian Henning wrote:
>> *rubs eyes*
>>
>> There it is, right in front of my face.  Thanks for not being a jerk
>> about pointing out the obvious to me. :-D  My excuse is "it's Monday."
>>
>> The question becomes, then, what is the output when the input is an
>> error?  Garbage or nothing?
> 
> By default, nothing.  It will only write as much of the block as you
> were able to read.
> 
>> I think it might make for a more difficult recovery (then again,
>> maybe it won't) if, for example, 100 good bytes + 10 errors [in] ==
>> 100 bytes out, instead of 110 bytes out (10 of which are garbage).
> 
> Quite right.  This is why you will also need the "sync" option to conv.
>  That will write NUL bytes in place of what would be garbage.
> 
> My references:
> http://www.macosxhints.com/article.php?story=20050302225659382
> dd(1) manual page
> 
> -- Kevin
> 

-- 
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Brian A. Henning
strutmasters.com
336.597.2397x238
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