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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