[mythtv-users] USB Hub Bandwidth limitations?

Brian Wood beww at beww.org
Wed Jul 8 00:53:56 UTC 2009


On Tuesday 07 July 2009 18:31:37 Lindsay Mathieson wrote:
> I want to plug 4 USB HD Tuners into a USB Hub - the hub itself has 480Mbs
> bandwidth.

You mean the box says 480 bandwidth, real world sustained USB hardware 
performance is generally somewhat short of that.

But I suspect you will be OK with 4 tuners.

The HDHR does a fine job over a 100-base-t network, not pushing it hard at 
all, so you should be OK with 4 tuners over USB, theoretically.

I'd be more concerned about your disk I/O, which should also be OK as long as 
things are running optimally. Turn off DMA and you're in trouble though.

Linux USB is not famous for efficiency, I'd guess that's the first place 
problems would start to show up, but that's just a guess.

>
> I'm guessing even if all the Tuners are recording multiple HD streams (via
> multirec) there won't be any problems as a HD stream max's out at around 30
> - 40 Mbs for good quality 1080p. Though this is Australia FTA so its more
> likely to be 720p at best, more likely 480i :)
>
> Additionally I guess the hub would need to be powered? or could an
> unpowered hub support 4 HD tuners?

I'd think that as long as the tuners are self-powered (not drawing power from 
the USB port), you would not need a powered hub, but it couldn't hurt.

-- 
Brian Wood
beww at beww.org


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