[mythtv-users] MythTV - Video Distribution Solution?

[Drew Tomlinson]

On 1/14/2008 11:07 AM MythTV wrote:
> Hi everyone!
>
> I am writing from the Hermon School Dept. and we are very interested in
> the possibility of using MythTV in our district.
>
> I've been through the documentation, but I have a few questions.
>
> In our case, we are not only looking for a simple DVR, but a network
> distribution utility.
>
> Our goal is to have a way for teachers to access recordings in their
> classroom through a "frontend" device, that would in turn connect to a
> central server with the video storage. It sounds like MythTV would support
> this. Also, teachers would need to be able to access cable and Satellite
> through the frontend.
>
> I do realize that a cheap server wouldn't work for this environment, and
> would be willing to purchase a high-end server to handle the capacity of
> the High School. (There would be a server in each building). 
>   

Actually, it is my understanding that you don't need much in the way of 
CPU horsepower for the backend server.  The backends don't do much more 
that connect to tuners and stream data to disk.  Thus, the backend(s) 
need to have large amounts of disk space and a I/O bus that can handle 
the data needs.  It really depends upon how much total storage you 
expect and how many simultaneous streams to expect to record and/or 
serve.  On my system, high definition content received over the air uses 
about 7 GB an hour.  Standard definition content is delivered to me via 
DirecTV tuners attached to WinTV PVR-250 cards via S-Video.  At my 
settings (basically the defaults as I recall) this content needs about 
2.2 GB per hour.  Thus this becomes a simple math problem:

(concurrent streams) x (avg. data rate) = I/O bus speed requirement

> My question is, how many frontend devices can a MythTV server support
> concurrently? At the high school, there would be about 45 classrooms with
> front end units. (Realistically, they all wouldn't be using them at the
> same time.)
>   

This is where you will need a higher end processor if you plan to 
distribute HD content as the frontends do the decoding.  However if only 
SD content, these devices don't need that much horsepower either.  I ran 
my first Myth box on a AMD Athlon 700mhz processor.  It was a 
backend/frontend combo that supported two SD tuners and it ran just fine.

> What would you say the specs of a server would need to be to support at
> least 10 frontends at the same time? The front end devices and the server
> would be on their own segment of a 1-Gig backbone network so bandwidth
> shouldn't be an issue.
>   

Again, the backend server is just streaming content to the frontends 
which doesn't take much CPU.  I'd be willing to bet an old 600 mhz 
Pentium III could handle the CPU load just fine.  However this is only a 
guess on my part.

See the math problem above and look at the specs of an old ATA-133 IDE 
card and the hard drives to see if it could move 22GB (10 streams x 2.2 
GB/hr) in an hour.  I suspect it could.

[deletia]
> Last, but not least, I see that MythTv supports adding multiple recording
> servers. Can we add a second recording server (or server with different
> sources) and integrate it with the overall program guide that the frontend
> use, or would the frontend machines have to be changed to point to a
> second server to see the programming available on it?
>   

I would consider building one low powered backend for every 4-6 tuners.  
I would also try and build them on identical hardware so I could 
maintain one image for all.  I might even see about net booting but I 
have never done this.

Hope this helps a bit,

Drew

[deletia]

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