[SATLUG] simultaneously burning multiple DVDs

Christopher Chavez chrischavez at gmx.us
Sun Dec 28 20:08:47 CST 2014


> On Sun, Dec 28, 2014 at 02:49:12PM -0600, Samuel Smith wrote:
> > On 12/26/2014 12:14 PM, Borries Demeler wrote:
> > >Recently a question has come up for which I do not have a good answer -
> > >does anyone have a good explanation for this:
> > >
> > >If one has multiple DVD writers installed and wants to make multiple
> > >copies of the same iso file by simultaneously writing them to all
> > >installed DVD writers, such an operation produces faulty drives.
> > >Furthermore, K3B does not allow writing to multiple drives - there must
> > >be a reason for that.
> > >
> > >I am trying to figure out where the bottleneck is. Initially, I suspected
> > >that the harddrive my not be fast enough to be read by multiple cdrecord
> > >instances. But copying the iso file to a ramdrive and burning with the
> > >ramdrive location as the source offered little to no improvement. The
> > >SATA drives (configured as a RAID) should not be a bottleneck. I measured
> > >the sustained read speed to be no less than 150 MB/sec.
> > >
> > >Is there is a solution so one can write to multiple writable DVD drives,
> > >and where is the bottleneck? Does anyone have experience with this
> > >particular problem?
> > >
> > >Thanks, and happy holidays to all! -borries
> > >
> >
> >
> > K3B is basically just a wrapper around several command line tools
> > that burn disks. You could I suppose, just run those commands as
> > many times as needed in parallel. Never tried it though.
> >
> > --Sam
> When I said "such an operation produces faulty drives" I meant to say
> faulty DVDs. Those faulty DVDs were created by running multiple instances
> of cdrecord, a commandline tool.  All works well when running one copy,
> but more than one simultaneous burn operation causes the bad DVDs (audio
> skips, for example). The problem gets worse the higher the number of
> simultaneous write operations, even when the source iso file is on a
> ramdrive. Just curious where the bottleneck is and what to do about it.

The bottleneck could be in how the DVD writers are connected. If I'm not
mistaken you have only mentioned how the hard drives were connected, and I
would agree that it is not a bottleneck in this instance.
How are the DVD drives connected? Depending on the burning speed, I've read
that an interface like a single PATA/IDE channel shared between two drives,
especially without an 80 conductor cable, or USB 2.0 DVD writers connected
through a hub, can lead to burn failure from buffer underrun. Some
drives/programs have an option to try using "buffer underrun protection"
provided by the DVD writer; in cdrecord (a.k.a. wodim, which are used by K3B),
this had to be enabled manually in older versions (driveropts=burnfree) but it
is now enabled by default. Some BIOSes have options that prevent PATA/IDE from
operating at the highest speeds supported by the drives, so those may also be
checked.
I'm not certain this always works, but probably the only workaround if the
DVD writer's interface is simply too slow is to force burning at a lower speed
(wodim speed=#). I think another way to possibly detect bottlenecks is to try
benchmarking the read speed from the burners individually and/or
simultaneously; this may identify a safe upper burning speed.
Cf. http://en.wikipedia.org/wiki/DVD#Transfer_rates and
http://en.wikipedia.org/wiki/List_of_device_bit_rates

-Christopher Chavez


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