Re: DVD Compatiblity issue

[Andy Polyakov <appro@fy.chalmers.se>]

> >The cdrecord README clearly states that you _need_ working DMA
> >in order to write DVDs. If you have burnfree ON the drive just
> >dramatically slows down.
> >
> >
> If the DVD unit were set to 4x, but data underrun were reducing the
> effective transfer speed to 2x,

Well, this I can agree with 100%, but I can't see that this is
equivalent to the referred statement. There is a huge difference between
"having burnfree ON" and "suffering from buffer underruns," as well as
between "*just* dramatically slows down" and "cause *effective* speed
reduction," don't you think?

Of course whenever recording suffers from buffer underrun, an idle spin
has to be taken, which effectively slows down the recording, but the
question is for how much. This was discussed already, given that DVD+
performs as expected at 2.4x (as on requestor's system), 3x seems to be
commonly observed value for 4x media in the lack of DMA, not 2x as user
reported. Also note that given that buffer capacity is enough to sustain
several rotations, the unit is capable to follow the wire transfer speed
without abrupt performance degradation (because proportion of idle spins
is minimized). I mean you don't normally end up in situation when
performance degrades by factor of N, whenever maximum transfer rate
between host and logical unit is only slightly lower than required.
Instead, you observe effective recording speed being slightly/somewhat
less than the actual wire speed. Well, this naturally does not exclude
the possibility that there might be firmware implementations out there,
which would exhibit abrupt performance degradation, in which case one'd
say "if recording suffers from buffer underruns, you *can* observe
dramatic performance degradation," but you can't say "it *just* does
it." 

> would cdrecord report the speed set or
> the speed achieved?

It prints both as far as I understand. Requestor should be able to
clarify which one, intended velocity in the beginning or average summary
at the end, he was referring to. Cheers. A.