[SATLUG] simultaneously burning multiple DVDs

Borries Demeler demeler at biochem.uthscsa.edu
Tue Dec 30 11:35:29 CST 2014


On Mon, Dec 29, 2014 at 10:38:41PM -0600, Othniel Graichen wrote:
> Are you looking for the reason or a solution?

Both, of course :-)

> A straight-forward solution is to reduce the Write speed and to use DVD
> burners with at least 2MB on-board memory buffers.

If I needed 2 MB on board memory buffer, does that ninux cannot supply
the data fast enough to the drive if I use more than one drive?

If so, the question comes up why Linux cannot do that. Assuming I use a RAM drive
as the source for the iso to be written to multiple drives, is it because the
RAM drive is too slow to be read?? That I find hard to believe.
So is it because the data cannot be moved fast enough through the system bus?
With Gbit bus speeds, I also find this hard to believe.
Is it because the CPU is too slow? I have multiple cores, each could run 
a separate process, so this can't possibly be the reason either.

I am still stumped why this doesn't work as expected.

> The linux cdwriting app is not written/designed to be run in parallel.  It

Of course I would run multiple instances of cdrecord or whatever app I am using 
to write the multiple copies. The OS should have NO TROUBLE whatsoever to run 
for example 4 copies at the same time.

> is designed to compensate for the small buffers on many early drives.
> Should the write buffer be depleted while another task is trying to fill the
> wrong buffer you have what is called a buffer underrun error.

Why would it run out of data? The data is coming from a RAM drive which can
feed data a whole lot faster than even 4 simultaneous DVD writers could consume!

This doesn't make sense to me...

-b.

> 
> On Sun, Dec 28, 2014 at 2:58 PM, Borries Demeler <
> demeler at biochem.uthscsa.edu> wrote:
> >
> > 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.
> >
> > -b.
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