[mythtv-users] Tuner Card w/ Svideo Inputs & PCI Sound Transfer

Kyle Rose krose+mythtv at krose.org
Fri Jan 23 14:42:48 EST 2004

> Let's say I was recording in MPEG4 @ 640x480, which is ~2
> gigabyte/hour or 4.55 million bits/sec times 4 streams = 18.2
> million bits/sec. According to Seagate a Barracuda 7200.7 SATA can
> handle an Avg. Sustained Transfer Rate of 32 - 58 million bytes/sec,
> or 256 - 464 million bits/sec. I was going to do a RAID0 so it seems
> like it could handle it. That doesn't include the loss of
> performance due to multiple streams being written, but I guess I'll
> just have to give it a shot and see what happens.

On a PATA 100 Seagate 7200 RPM drive on my single Athlon 1800+ in
super-duper hdparm mode (-c 3 -d 1 -u 1 -m 16 -X 69), I find that
writes max out at about 20 MBytes/sec when things are tweaked (bdflush
set to flush dirty buffers once per second instead of once every
thirty seconds, for instance).  So, I'd be surprised if you got more
than 32 MBytes/sec on SATA, even at its maximum transfer rate (166?).

Still, 32 MBytes/sec should be way more than sufficient for four
*ATSC* streams (HDTV), which produce about 2-1/2 MBytes/sec.  When I
get around to doing HDTV, I don't expect to run into any drive or bus
width limitations.

> The PCI bus will brobably get the workout. Thanks for the tips! They're been
> very helpful.

Even "slow" 32-bit, 33MHz PCI will do 130 MBytes/sec, at least as much
as four SATA drives can do.  The biggest wildcard is the capture
cards: MPEG/ATSC cards produce a miniscule amount of data compared to
the width of PCI, while simple frame grabbers could easily clog it.


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