Subj : ddrescue
To   : Dumas Walker
From : Arelor
Date : Tue Feb 09 2021 03:17 am

  Re: ddrescue
  By: Dumas Walker to ALL on Mon Feb 08 2021 03:45 pm

 > I have been trying to use ddrescue to make a good copy of a DVD that only
 > works in some of my DVD players.  I actually got it to work with one DVD,
 > but the other one gets so far and then, after several hours, the screen
 > looks like this:
 > 
 >  ***
 > # ddrescue -v -b 2048 -r 4 /dev/sr0 D1.iso D1.log
 > GNU ddrescue 1.23
 > About to copy 7255 MBytes from '/dev/sr0' to 'D1.iso'
 >     Starting positions: infile = 0 B,  outfile = 0 B
 >     Copy block size:  32 sectors       Initial skip size: 64 sectors
 > Sector size: 2048 Bytes
 > 
 > Press Ctrl-C to interrupt
 >      ipos:    4415 MB, non-trimmed:  360116 kB,  current rate:       0 B/s
 >      opos:    4415 MB, non-scraped:        0 B,  average rate:   79775 B/s non-tried:    1716 MB,  bad-sector:        0 B,
 > error rate:    8192 B/s
 >   rescued:    5179 MB,   bad areas:        0,        run time:     18h  2m
 > pct rescued:   71.37%, read errors:     5569,  remaining time:         n/a
 >                               time since last successful read: 16h 30m 43s Copying non-tried blocks... Pass 5 (forwards)
 >  ***
 > 
 > Note that the last successful read time is over 16 hours.  At this point,
 > the numbers in the left column have long since quit incrementing, while the numbers (that are not 0) in the other two colums
 > are the only ones going up.
 > 
 > I have searched on the internet about this.  Some folks talk about theirs
 > going days without ever stopping on its own.  Others point out that
 > sometimes you can CTRL-C out and the iso you get will be mostly OK.  Mine unfortunately was not.  :)
 > 
 > Is there anything I should think about changing on the command line to get better results?
 > 
 > 
 >  * SLMR 2.1a * I am Popeye of Borg. Prepare to be askimilgrated.
 > 

I don't do a lot of optical media rescuing with ddrescue, but the idea is that you have to perform the reads using multiple
devices.

Say you have a bunch of defective sectors. Some optical media reader is  capable of reading 33% of them. Another media reader
can read 50% of them. And another media reader can read 39% of them. Hopefully if you run ddrescue with each reader, and put
the results together, you can rebuild the whole iso or at least the most of it.

You could run a round of reads using the -n switch, which should speed things up quite a bit. Reduce the number of retries too
- there is no point in trying 4 times for the sector in a first run. You will retrieve less data with each pass, but the thing
is that if 30% of the image is unreadable after the first run you know you can put the DVD into the trash and need waste no
more time :-)


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