[mythtv-users] How to force frontends to play only from master backend?

[John Finlay]

Harry Coin wrote:
> Michael T. Dean wrote:
>> On 03/15/2009 05:08 PM, Nick Rout wrote:
>>> On Mon, Mar 16, 2009 at 9:42 AM, William 
>>> <william_munson at comcast.net> wrote:
>>>  
>>>> Harry Coin wrote:
>>>>   
>>>>> Using 0.21 I need help to cause frontends to play from the 
>>>>> 'masterbackend'
>>>>> only, even though diskless other slave backends that received and 
>>>>> stored the
>>>>> shows are running on the same little net.
>>>>>
>>>>> I have some older, slower diskless PC's acting as slave backends.  
>>>>> These
>>>>> were just supposed to catch the video and put it on the common nfs 
>>>>> share,
>>>>> never host playbacks.   There is a master backend that has an NFS 
>>>>> share that
>>>>> all the frontends and backends can access.  The masterbackend is 
>>>>> fast, has
>>>>> quick disks and has a fast network connection.
>>>>>
>>>>> But, I've proven that the frontends actually don't actually pull 
>>>>> from the
>>>>> master backend either stream or nfs, but contact the slave backend 
>>>>> that
>>>>> recorded the video, cause that little underpowered thing to pull 
>>>>> the video
>>>>> from the nfs share, then stream it out to the frontend.    So, bad
>>>>> performance, choppy playback, dropped frames on recording and so on.
>>>>>
>>>>> So, I really need to turn off any kind of playback activity / 
>>>>> streaming
>>>>> from all the diskless slave backends - but to have them still be 
>>>>> running to
>>>>> host the tuner cards and record shows.   Help please!
>>>>>
>>>>> Last, I'd appreciate some guidance about whether the frontends 
>>>>> would do
>>>>> better to use NFS to playback from the server, or cause the server 
>>>>> to stream
>>>>> -- and tell me how to direct the frontends to implement that 
>>>>> decision.
>>>>>       
>>>> There is an option to always stream from the backend with a check 
>>>> box on one
>>>> of the setup screens, Sorry but I am not able to get to the system 
>>>> right now
>>>> to give the specifics
>>>>
>>>> I think its in mythtv-setup rather than the frontend setup.
>>>>     
>>> I think its in frontend setup as I just noticed it when setting up a
>>> new frontend yesterday.
>>>
>>> However I am not sure that it achieves the aim of "always stream from
>>> the MASTER backend rather than the backend that recorded it"
>>
>> Right, Nick.  The mythfrontend setting is:
>>
>> Always stream recordings from the backend
>> Enable this setting if you want MythTV to always stream files from a 
>> remote backend instead of directly reading a recording file if it is 
>> accessible locally.
>>
>> and it makes the recording host stream the show.
>>
>> There's also the mythtv-setup setting:
>>
>> Master Backend Override
>> If enabled, the master backend will stream and delete files if it 
>> finds them in the video directory. Useful if you are using a central 
>> storage location, like a NFS share, and your slave backend isn't 
>> running.
>>
>> but that would only make the master backend stream the files if you 
>> shutdown the recording host.
>>
>> However, if you have a "local" copy of the file available to the 
>> frontend--i.e. a copy of the file on a filesystem that's directly 
>> accessible by the frontend (which means NFS mounts are "local")--the 
>> frontend will read the file directly from the disk (which would mean 
>> from NFS).
>>
>> In your test, it didn't do so because you either had enabled the 
>> setting, "Always stream recordings from the backend", or your 
>> filesystem is using a different structure on the frontend from the 
>> backend(s).  So, uncheck that option and/or make the directory 
>> structure of the recording directories /exactly/ identical on /all/ 
>> hosts (backends and frontends), and all will work.
>>
>> Mike
>>
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>>
> Thanks to all for these insights.    To sum it all up, when is more 
> than one backend but only the master has fast disks holding all the 
> files and fast networking there are two choices.
>
> A:  Preserve the benefits of mythtv backend streaming, avoid exposing 
> the filesystem to the frontends via nfs, presumably gain the benefit 
> of whatever other frontends may speak the streaming protocols all by 
> ferreting out a mysql update command to cause all shows to point to 
> the master backend as the source for all shows and running it on a ten 
> minute schedule as a cronjob.
>
> B:  Turn off the 'always stream' setting in the frontend, turn off the 
> 'master backend can stream if the others are taking a nappy' setting 
> in the backend, export the source of all files to the frontends via 
> nfs in exactly the same access path fashion as the backends use to 
> write them.  Then the frontends will default through and use nfs to 
> play the shows defacto fetching them from the nfs servers running on 
> the master backend.
>
> I think on balance 'A' is the better choice to keep overall complexity 
> down as far as hacking settings on frontends re: nfs and overall 
> maintainability.    I think changing the backend setting from a toggle 
> to 'stream from master if slave backends are sleeping or not' to a 
> three state:  'always stream from master backend when possible, only 
> if slave is snoozing, never' would be better! 
> Thanks all again
>
> Harry
If you have videos you have to set up NFS access on the frontends to 
play them which tips the balance to scenario 'B'.

John