[mythtv-users] CPU power for digital tuners

[Jarod Wilson]

On Friday 09 July 2004 17:01, Dylan Egan wrote:
> > On the other hand, general throughput (e.g. PCI bus, HDD) might become a
> >problem. Here in Oz, SD broadcasts are about 6Mbit/s, and I think HD are
> >10-12. If you've got a few cards recording HDTV at the same time, you'll
> >want to make sure you've got a pretty quick disk subsystem.
> >  
>
> Hrmph yeh I didnt really consider that. Im using that machine as a file
> server too, it used to be a mail/web server too, but I moved that to
> another machine. Maybe I can have 2 machines splitting 4 cards or so, so
> 2 in each. Im running 1 SATA drive at the moment.

Typical US ATSC HDTV streams are usually 19.2 Mbps (though they can be 
greater). Any reasonably new hard drive has a sustained throughput threshold 
magnitudes greater. SATA has a theoretical peak of 150MB/s. Low-balling it, 
sustained transfers might be in the 60MB/s range, which still translates to 
480Mbps. So you can write several HDTV streams at once. I know someone who 
has 3 pcHDTV cards that has no problem recording 3 streams at once on a 
single 5400rpm drive.

In short, if you're talking 10-12Mbps streams, your single SATA drive 
shouldn't have a problem handling all four cards. That'd be a peak throughput 
requirement of 48Mbps, which is hardly going to make the drive sweat. At 
least theoretically. (Some of the Linux SATA drivers still absolutely suck).

-- 
Jarod C. Wilson, RHCE
jcw at wilsonet.com

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