[mythtv-users] Diskless

[Johan Braeken]

Quoting Richard Stanaford <rstanaford at gmail.com>:

> --- Original Message ---
>
> I came across the diskless how-to on the Wiki and, while I have the
> entire infrastructure in place (I build both windows and Linux boxes via
> PXE booting), I immediately thought "hey, that would definitely be QUIET".
>
> However, the question that goes unanswered in the wiki is about
> performance. Since the entire system is loading and running off of the
> network (I've got cat-5 wired) *and* mythtv is also going over that same
> network, doesn't that beat up on the performance? Especially since swap
> would also be on an NFS mounted volume...
>
> I'd be interested to hear about people's experiences with MythTV and a
> diskless frontend to see if it would be a viable configuration or if it
> is just a pipe dream..

I have a MiniMyth frontend.
It is booting with PXE and running entirely in RAM (512Mb, no swap)
Videos and Music are accessed via NFS.

Working perfectly!
I even have all my DVDs in iso format on the server so I can watch them.

I also run LTSP on the same network and network speed is not an issue for me.
Even when doing massive filetransfers, close to the maximum  
theoretical network speed, Mythtv keeps running smoothly.


I have to say I have a Cisco switch, which will probably perform  
better than a "entry-level" model. But, even then, I would not expect  
problems due to the slow network speeds actually required as explained  
below by another poster.

So I would say, running MythTV, even with multiple clients, over the  
network is not a problem at all.


Cheers,

Johan.


> --- End Original ---
>
> Hi Rich,
>
> If your network is 100 Megabit-switched, you should have nothing to worry
> about, even if you want to stream HDTV.  Consider that under most
> configurations, HDTV encoding will commit up to 9GB per hour of video.  Nine
> gigabytes (or approx 9000MB) per hour is approx 150MB/min or 2.5MB/sec of
> data.  Well, we measure data (disk size) in Bytes (big B), but network speed
> is usually measured in bits (or bits per second, little b).  So, in order to
> smoothly stream HDTV to your frontend, you would need to be able to sustain
> 20Mb/sec (2.5 * 8, where there are 8 bits in a Byte), which is a cinch for
> 100Mb-switched, assuming everything is running at full duplex.  When
> transferring file between my machines, my network routinely sustains
> 80Mb/s.  And since it's full duplex, that means 80Mb/s transmit and 80Mb/s
> receive at the same time.
>
> So, the bandwidth is there.  Since the worst you can likely do is stream an
> HDTV from each frontend, the only consideration is the common network
> segment, which is your backend to the network switch.  Say, for example, you
> wished to stream three HDTV streams to three different frontends.  Each
> frontend would put 20Mb/s on its own link to the switch which would
> aggregate to about 60Mb/s throughput for your server.  You're not likely to
> ever do that, but I wanted to use that as an extreme example.
>
> With a sufficient amount of RAM, you are not likely to have to NFS swap from
> the frontends, even with 256MB of memory, especially if you are doing
> hardware decoding.  The output from come through the network interface,
> across the bus to the decode hardware of your video card (or chipset), so
> there's really nothing to buffer.  Unless you have stuff running on the
> frontend box other than just MythTV, there should be nothing to swap
> either.  But even if it had to, your network would have to be taxed
> virtually to its "knees" for you to notice it.
>
> I hope this helps a little.
> -Rich.