This sounds like a bad head. If the slow sectors are unreadable
(errors) then you can adjust the skip size. With ddrescue 1.19 you
could add the option --skip-size=25Mi,50Mi (if I have the format
correct). That will skip 25MB on the first error, with no more than
50MB skipped on each consecutive error. This will skip out of the bad
head faster than normal and allow more reading of the good data first.
If the disk has 2 platters then it has 4 heads, and 600MB of good read
would be 3 heads of 200MB chunks, and a bad head of 200MB. This is an
estimate without knowing what drive you actually have or the number of
platters. So in theory the added option would skip out of the bad
chunk after no more than 8 errors. On the reverse pass any trailing
data that was skipped is picked up. I have bench tested this method
and it has good results. Head movement is linear, and the data from
the good heads is recovered much faster. Once it gets past the copying
phases and starts the trimming phase and scraping phase expect it to
be much slower as it is dealing with the bad head, and other than
being patient and waiting for the recovery to finish (or the drive to
die), the only other option is take it to a professional.
I forgot that there are 3 passes with ddrescue 1.19. The 3rd pass is
without skipping and will also be slow. With the correct options and
skip size, the first 2 passes (forward and then reverse) are the
important ones to get the data from the good heads.
Scott
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