brand-new DVD drives less reliable than crappy old player - fix?

Ted Mittelstaedt tedm at
Sat Feb 9 03:55:54 UTC 2008

> -----Original Message-----
> From: owner-freebsd-questions at
> [mailto:owner-freebsd-questions at]On Behalf Of Steve Franks
> Sent: Thursday, February 07, 2008 10:55 AM
> To: User Questions
> Subject: brand-new DVD drives less reliable than crappy old player -
> fix?
> I have a bunch of disks that will play fine in my laptop and TV, but
> not in my freebsd system with a new-ish NEC drive.  Figured it was the
> drive, so I got a new pioneer, same issue - scratch somewhere that
> causes no hiccup on other players makes it tank.  I can't even cp or
> rsync data off them, and these are only minor scratches.  Is there
> anything tunable, or ways  to keep rsync or cp going after an error?
> I get 100MB of the last GB file.  Most annoying.  I know you usually
> want cp to fail if there's read errors, but this is one instance where
> you'd like it to skip and keep going - I assume that's what my dvd
> player does.  These are not commercial disks, so I can't just go out
> and buy a new one, and I was too stupid to make backups, so I have a
> vested interest in a workaround.

The newer drives turn the disk faster, so of course there is less time
the laser light is shining on the spot where the data is, and if a
scratch has damaged that spot then optically the bit is not fully 1
way or fully the other, so the voltage out from the laser's eye is
going to be closer to the "undefined" range.  What is coming out
of the laser's eye is effectively a "dirty" square wave.  I think
the developers of the faster drives decided to reduce the sampling
window that they look for a logic high or a logic low, so they can
sample the bit closer to the center of the high or low, and also
since the sample time is lower, they make the circuit less tolerant
of bits that are a little less "high" or a little less "low" coming
out of the laser's eye.


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