[SATLUG] simultaneously burning multiple DVDs

Craig sargonemail at gmail.com
Wed Dec 31 02:02:15 CST 2014


*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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