simultaneous copy to multiple media

[Diez B. Roggisch]

> 2) if I understand it right, an USB controller is connected to
> to the PCI bus and there can be many separate USB
> controller on one PC

True.

> 3) the theoreticall speed of USB (430 MByte/s?) is much
> higher as the experienced 15 MByte/s, probably due to slow
> controller on the side of the external storage media, so
> maybe even on one USB line I will have the chance to
> use it full capacity connecting many slow devices
> (I can't imagine, that USB goes down with the speed to
> the speed of the slowest component connected, does it?)

Nope. Or yes. Here comes into play why Heiko said think of what USB stands
for. While the devices appear to be responsive concurrently (the bus
arbitration and multiplexing/demultiplexing is tranparent to the user), it
still is  a serial bus, so at a given point in time you can only write to
_one_ device. And if that device is limited in its speed, you're doomed.
The only thing I could imagine is that if you send small bursts that don't
make the write cache full, it _might_ be possible to switch fast between
the devices and thus write the data faster, as the devices can try and
write the data to disk while the others are feeded. 

But I'm on no sure ground here with that assumption, and it certainly would
depend on how the usb-ata-controller deals with that. You said yourself
that you only had 15MB/sec, so it doesn't look to good.

To make this work would certainly be a deep lowlever driver hack and nowhere
in the scope of python per se.

> 4) with 45 MByte/s I could theoretically simultaneously
> supply three separate data streams to three USB
> controller writing with 15 MByte/s each out to the
> external storage media.

That might be the case if you use three real separate controllers. But that
will depend on how the OS deals with these, if you really achieve the
theoretical throughoutput.

> 5) watching the low CPU usage while writing to USB
> shows me, that CPU-time is not a problem.

That is certainly true - the bottleneck are the buses.

-- 
Regards,

Diez B. Roggisch