[mythtv-users] Master Backend Override Confusion

Bruce Markey bjm at lvcm.com
Thu Mar 31 20:52:55 UTC 2005

dfleming at swings.2y.net wrote:
> I just added a third tuner to my system and while I have been using 
> myth for some time now, this darn "Master Backend Override" switch is 
> confusing me.
> I have 3 PCs all with 1 tuner card:
> System1 - Master.  Frontend/Backend, has large disk allowing NFS.
> System2 - Slave. Diskless Frontend/Backend connects to Master via NFS.
> System3 - Slave. Diskless Frontend/Backend connects to Master via NFS.
>>From what I understand, the "Backend" that created the recording also 
> streams the given recording to Frontends local and remote.  In the event 

not necessarily...

> that the "Backend" that created the recording is unavailable, the 
> "Master Backend" will look for the file and, if found, stream the file 
> to Frontends if "Master Backend Override" is enabled.


> If everything is correct so far, here are my questions:

Robert can correct me if I've forgotten something here.

First, the frontend looks to see if there is a RecordFilePrefix
for it's hosts and sees if the requested file is there. If so
it reads the file from the filesystem.

If not, the frontend asks the master backend which host's backend
to connect to to get the stream. The master may serve the file if
recorded the file itself or defer to the slave that did record it
and has it locally.

MBO say that you are using NFS and all the files are expected to be
physically located on the master backend. In that case, there is no
reason to tell another slave to read the file over NFS just to
stream it out again over the network a second time. Therefore, MBO
tells the master to serve all the files requested whether or not
the slave is available. Also, because the files are local, the master
should delete them itself whether or not the slave is available
rather than asking a slave to do a remote delete over NFS.

> Should "Master Backend Override" only be enabled on the "Master"?

There is one global setting, it is not per host.

> Are there any ways to minimize network traffic?

I always use local disks for each backend so that recording doesn't
have to go over the network and for other reasons.

> I would rather have my Master system stream all recordings.  Otherwise 
> it sounds possible that a Slave could read the file via NFS, then stream 
> the file to a remote Frontend thus doubling the network traffic for 
> streaming 1 recording.

MBO is precisely for preventing that.

--  bjm

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