[lug] disk image with dd

Ben bluey at iguanaworks.net
Wed Jul 15 16:58:34 MDT 2009

> There were no errors which is a pleasant surprise, so I should have a 
> duplicate copy of all the data on hdd.  Looking at the web site for 
> dd_rhelp, it says "The gaps that aren't already parsed with dd_rescue 
> are filled with zeroes."  I suspect I may have some deleted files on hdc 
> that I'd like to try and recover.  Am I reading this correct that I 
> won't be able to recover any deleted files on the destination drive, 
> hdd, as all gaps will be written with zeros?
dd_rhelp and ddrescue and dd know nothing about the filesystem, deleted 
files, etc. They just read 0's and 1's. The text you quoted, I believe, 
is when you have errors, dd_rhelp jumps forward to (hopefully) a spot 
without errors and it fills in the gap with 0's. This makes sure the 
output is the same size as the input even if it can't read all the 
data.ddrescue, I think, might just skip the area, resulting in a smaller 
file and that he data positions of the "copy" isn't the same as the 
original (and dd just stops). Since you have no errors on the 
filesystem, dd dd_rhelp and ddrescue would all produce the same thing -- 
an exact copy of the your filesystem. As for recovering deleted files, 
that depends on the filesystem, what has changed on the filesystem since 
you deleted and files and is above my knowledge. But if it is possible 
to get the files back, you can get them back from the copy you just made.


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