[mythtv-users] Two mythtv machines and confusion

Michael T. Dean mtdean at thirdcontact.com
Thu Nov 19 06:57:10 UTC 2009

On 11/19/2009 01:28 AM, stan wrote:
> I have two machines (call them A and B) running mythtv independently.  The
> each consider themselves as the master backend.
> Machine A is sitting next to the TV and will be used for real playback.
> It's recording input will be QAM from a raw Cox cable TV feed split ahead of
> the set top box.  Hopefully, I can get program guide information from clear
> QAM channels themselves.
> Machine B is in another room and drives a small monitor.  It's location
> allows for good OTA reception so it's recording input will be OTA ATSC.
> Program guide information will be from the ATSC stations themselves. I might
> watch recordings on the small monitor from time to time.
> I'd like to connect the machines, making one a master backend and one a
> slave backend.  I think I want to store all recordings on machine A because
> it might be better to have the programs on a local disk for playback.
> Questions:
> 1.  Which machine should be master and which should be slave?  Does the
> master need to be running to play back on a slave?  I'd like to avoid
> powering on machine B just to play back from machine A.

There is only one master backend.  The master backend must be running 
for the remote backend to work and must be running to use /any/ MythTV 
client (mythfrontend, MythWeb, scripts using the Perl or Python bindings 
(though some may operate in a "disconnected" mode where they don't 
really do much of anything)).

> 2.  Where is program information stored?  All in the master machine's
> database, or some in each?

All in the same database.  It doesn't matter what host runs the MySQL 
server--only that all mythbackends and mythfrontends and MythWebs talk 
to the same MySQL server and use the same MySQL database.  There's only 
one database in any MythTV system.

> 3.  Where is the recorded program information stored (file pointers,
> commercial flagging, etc.)? All in the master machine's database, or some in
> each?

Only one database...

> 4.  Can I somehow tell mythtv to store all programs on machine A, or do I
> force this with appropriate NFS mounts?  If I do use NFS mounts can both
> machines point to /media on machine A?

All backends require "local" access to storage for writing recording 
files.  You may use NFS to make a remote file system available locally.

> 5.  If channel numbers turn out to have conflicts between the two sources
> (cable QAM and OTA ATSC), will I be able to tell which is which?  Is this
> where the "source name" is used that mythtv never had to show me before?

Channel numbers are user-editable data (that's really only used for 
display purposes and to allow you to tell Myth to change to a specific 
channel in LiveTV by typing in that channel's number).  Just change the 
channel numbers if any overlap and you want to distinguish between them.

Note that if the content on the channels is identical, you can give them 
the same callsign and same channel number and they'll be treated as the 
same channel and shown only once in the EPG.

So, there is only one database per MythTV system ("system" of one or 
more backends and frontends and MythWeb hosts), and the master backend 
must be running any time you want to use any of the TV functionality of 
MythTV (you can use frontend plugins without running the master 
backend), and backends need local file system access to write out 
recording files (and locally-mounted remote file systems work fine)


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