[mythtv-users] The purpose of a Secondary Backend is...

Brad DerManouelian myth at dermanouelian.com
Fri Jun 20 02:55:08 UTC 2008

On Jun 19, 2008, at 7:06 PM, glenhawk at optusnet.com.au wrote:

> ...well I thought I knew but now I'm not sure. Is there any  
> documentation somewhere discussing the virtues of Secondary Backends?
> I figured that a Secondary Backend was there to take some load off  
> the Master but other that additional recordings I wasn't sure what  
> they were for.

Yes, taking load off the backend is one reason. You can have a lot of  
disk I/O from multiple recordings/streaming/transcoding, etc. Another  
reason is if you use PCI capture cards and you've run out of room.  
Heat is another an issue when you start adding a lot of capture cards.  
Serial ports are often hard to come by on modern motherboards, too. I  
had set up two backends because they both only had 1 serial port each  
and I needed to control both my STB's with the serial port.

The most important reason to use a slave backend is choice. Making  
MythTV a distributed system means that you can use whatever hardware  
you have around in any way you choose to use it.

> I have found since that it is possible to run the database on a  
> Secondary Backend but other than that...?

You can in fact run the database on ANY machine on your network. MySQL  
is a server/client application. It doesn't matter where the server is  
as long as the client can connect to it. You can run your database on  
another continent and it wouldn't matter as long as permissions were  
set up correctly and you didn't mind waiting a long time for database  
queries. :)

> I was interested to know if a Secondary Backend could run  
> independently from the Master. EG, can you switch on the Secondary  
> to watch something it recorded without having to have the Master on?
> I think I have found that you can't do that, it needs to see the  
> database to be able to run, is that correct?

No. When a slave backend starts, it tries to connect to the master  
backend. If it can't, you will get errors or if you have it configured  
incorrectly, it will start up as a master backend and give you even  
more problems.

> If so, that is a shame because I was hoping I could create a  
> portable PC that I could lug around to other peoples places or  
> functions to watch recorded TV (sporting events, movies, etc). If it  
> was easier to export recorded TV to AVI then I'd probably just do  
> that but HDTV is just so pretty ;-)



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