[mythtv-users] Disk utilization on slave backend questions

Bruce Markey bjm at lvcm.com
Fri Jul 8 19:25:38 EDT 2005

Alex Brekken wrote:
> One question Bruce about the NFS thing.  Just so I'm understanding
> this correctly, I don't need NFS drives in order for my combo
> frontend/backend to be able to play a recording which was recorded on
> the slave's local drive, correct? (including live TV)

>  NFS would only be necessary if I wanted to have the slave WRITE the
> recording to a non-local drive...?

Correct. Playback can go over a socket between a backend and
frontend but there is no socket for one backend to send data
to another backend to write the file (nor should there be).
Mythbackend just needs a path to a writable directory.

> In other words, the master backend knows how to get data from the
> slave backend without requiring NFS.

Master and slaves don't actually send recording data file content
between each other. It is when a frontend wants to do playback
that the magic happens. Say you have master "A" slave "B" and
slave "C" each with local disks. You sit at host "C" watching
the frontend and you select a show that happens to have been
recorded on "B". The frontend asks the master 'hey, where can
I find this file?' The master says it is on "B". The frontend
on C then opens a socket to the backend on B who starts sending
the data. These two myth processes negotiate a "read ahead buffer"
that sends data ASAP while playback is going on until it gets
two MB ahead.

Next let's say you pick a show that was recorded on "C". You
would think it would go through the same steps again to connect
to the local backend. However, the frontend cheats. It first looks
to see if there is a prefix directory setting for it's hostname.
If so, it checks to see if the file is there and will open the
local file without going through any backend (this is a good thing).

Because the frontend can read a local file or do smart application
specific buffering for remote files, you don't need NFS for

--  bjm

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