[SATLUG] simultaneously burning multiple DVDs

Borries Demeler demeler at biochem.uthscsa.edu
Wed Dec 31 11:44:01 CST 2014


Just to be clear:

Each writing process would be done with its *own* software instance. So
if I had 4 drives I would start 4 instances of the writing software
(each reading from the same RAM drive source), and each dedicated only
to a *single* drive.  None of the software instances would be required
to pass data to multiple drives and multiplex several data streams,
*except* of course the Linux kernel.

I believe Brad pointed out that the driver (part of the Linux kernel)
may have a limitation of only being able to buffer a small amount of
data, insufficient for supplying each cdrecord instance with sufficient
data to keep the writing process going smoothly? So, do I understand
correctly that the problem is not with the writing software (cdrecord), 
but a fundamental limitation in the Linux kernel's DVD driver module?

Thanks for everyone's comments, and happy New Year to all!

-borries


On Wed, Dec 31, 2014 at 10:27:59AM -0600, Kevin Buckner wrote:
> Software does not always take advantage of the capabilities of hardware.
> Just because the system has enough RAM doesn't equate the peripherals
> software is taking advantage of it. The system bus also is not a factor in
> it because again the device driver software for either the DVD controller
> or DVD authoring software may not be on par with hardware. A device
> controller on the hardware maybe able to daisy chain several devices but
> the driver software may access in a sequential read write.  Otherwise the
> driver software may not be up to par in reading writing to several devices.
> On Dec 31, 2014 8:13 AM, "Borries Demeler" <demeler at biochem.uthscsa.edu>
> wrote:
> 
> This machine has 32 GB RAM with a 5 GB dedicated RAM drive. No swap
> file/partition
> is set up, so it won't happen.
> There should be more than enough RAM to run the system without swapping.
> Again, I cannot fathom that the limitation is in reading the source file.
> 
> -b.
> 
> On Wed, Dec 31, 2014 at 02:02:15AM -0600, Craig wrote:
> > *Borries Demeler* on  *Tue Dec 30 11:35:29 CST 2014 *wrote:
> > >  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.
> > Are you absolutely sure the ram drive is non-swappable?
> >
> > If the ram drive or portion there of gets sent to disk swap (e.g. the
> > portion not yet burned,
> > but not in use), then needs to be swapped back in from disk (or portions
> > there of) when it's time
> > to be used, actual physical ram read access might not happen in time for
> > the buffer to be sent data
> > in time to  prevent buffer underrun.
> > -- particularly if swap is on a platter drive and/or other things are
> > jockying for use of the remaining
> > hard ram (e.g. swapped between swap space & physical ram).  Obviously in
> > this case, DVD data transfer
> > will be slower/lower priority than swapping between physical ram / virtual
> > ram.
> > Even if the ram drive is marked as "do not swap out of physical ram",
> > without a real time kernel,
> > swapping programs between physical ram & swap space can easily create
> > enough timing issues
> > which would destroy any advantages gained by the non-swappable ram drive.
> > So, having a ram drive may actually make things worse.
> > A non-real time kernel does not guarantee availability of resources at a
> > fixed point in time.
> >
> > ** try opening multiple tabs under a web browser, where each tab has a
> > youtube or flash media link.
> >     How many does it take before the active tab video starts skipping?
> > (take a look at vmstat / available memory & swap usage)
> >     How many tabs does it take before it becomes a chore to switch between
> > tabs? (take a look at iostat e.g. swap usage! ).
> >     How many open/active tabs before the web browser crashes under the
> > strain?
> > --
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