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[Bug-ddrescue] Rescueing CDs burned with Track-At-Once

From: John Bokma
Subject: [Bug-ddrescue] Rescueing CDs burned with Track-At-Once
Date: Fri, 29 Aug 2014 20:57:48 -0500
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.0

Dear all,

I am trying to archive CDs that were burned years ago. I noticed that:

ddrescue -n -b2048 /dev/cdrom cdimage logfile
ddrescue -d -b2048 /dev/cdrom cdimage logfile

Current status
rescued:   667650 kB,  errsize:    4096 B,  current rate:        0 B/s
   ipos:   667652 kB,   errors:       1,    average rate:     565 kB/s
   opos:   667652 kB, run time:    1.88 m,  successful read:      52 s ago

Based on what I've read those are most likely 2 blocks created by
Track-At-Once: "two unreadable run-out blocks at the end of the track."

isoinfo -d -i /dev/cdrom


  Volume set size is: 1
  Volume set sequence number is: 1
  Logical block size is: 2048
  Volume size is: 325851
  Joliet with UCS level 3 found
  NO Rock Ridge present

And gives a warning: Joliet escape sequence uses illegal space at offset
3. Can this warning be ignored?

Based on the above I calculate the size of the ISO image as: 32581 x
2048 = 667342848

The rescued image, however, is 667650048 bytes; 307200 bytes larger, or
150 blocks. Is this also a side effect of Track At Once?

Should I use the --size option (on both) to just grab the blocks as
reported by isoinfo?

Expected iso size: 667342848
dd if=/dev/cdrom bs=2048 count=325851 of=dd-CA19971201.iso
7a2be2b8e83f502dcd675cc39aca718f *dd-CA19971201.iso

ddrescue -n -b2048 --size 667342848 /dev/cdrom ddrescue-CA19971201.iso
ddrescue -r 5 -d -b2048 --size 667342848 /dev/cdrom
ddrescue-CA19971201.iso ddrescue-CA19971201.iso.log

7a2be2b8e83f502dcd675cc39aca718f *ddrescue-CA19971201.iso

So dd and ddrescue give me an identical iso. The big question is, am I
at risk at losing data by specifying the size?

Thanks for reading,

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