[mythtv-users] OT: Virtualization

[Simon Hobson]

Raymond Wagner wrote:
>> is incorrect is very easy to pass pci devices.
>
>The LinuxTV driver developers would disagree with you. Many times have 
>they tried to diagnose strange behavior on some user's system, only to 
>discover they were attempting hardware passthrough in a virtual machine. 
>Hardware drivers make certain, entirely reasonable, assumptions about 
>the behavior of the hardware they are interfacing with, and attempting 
>to use hardware in a virtual machine often invalidates those assumptions.

Been there :(

I ran my first Myth system as a Xen guest on a fairly low powered machine, with one HVR1200 tuner. It worked, mostly, but it couldn't record two programs (Multirec on UK DVB-T), commflag, and playback at once without corrupting recordings.

Then I saw HP doing their Microservers with £100 cashback which made them very attractive. My intention was to load it up with 8G of RAM, and run everything on one box - but the HVR1300 tuner didn't work. After some debugging, I found that with Xen loaded and more than 4G of RAM in the machine, it didn't work - the card was found, but no data could be received.
In the end I just bought another Microserver and did away with the hassle !



It depends on what you do, but Myth places significant real-time constraints on system performance which don't really apply to most other tasks. If you web or mail server is "slow" then pages/mails just take longer to process - if your Myth server is too slow (at least for I/O) then you get stuttery playback or even corrupted recordings. It's annoying if you are watching TV and it starts to stutter because someone's sent you some big emails and Amavis is chewing through them.
Most of this can be worked around, but by the time you've learned how to twiddle the various settings, it's easier to have another box.

One thing waaaay down my list of things to try is to put the Myth master backend as a Xen guest on the main box, and then start playing with the sleep when idle options for the Myth box. I don't see me finding time for that any time soon.