[mythtv-users] Combined FE/BE using USB for all I/O?

Eric Sharkey eric at lisaneric.org
Mon Aug 18 19:56:09 UTC 2014


On Sun, Aug 17, 2014 at 10:17 PM, Jean-Yves Avenard <jyavenard at gmail.com> wrote:
> A typical failure isn't due to the TFW (ThreadedFileWriter) taking too
> long to write, recordings pretty much always succeed unless you have a
> major hardware fault.
>
> A typical issue is the combination of the frontend + backend and
> attempting to watch an in-progress recording or liveTV.
> The frontend request data from the backend. While the backend is happy
> to write data in a non-blocking fashion, the read on the other hand is
> blocking, and there timeouts will occur if you have a bottleneck
> somewhere.
>
> Hope that clears things up.

Yes, it mostly does, thanks.  What you describe sounds pretty good to
me.  I still don't like ring buffers in general, but as long as the
writes are asynchronous and the sync's don't rely on the ring buffer
it really should be ok in practice.

But can you explain why multiple people on this list seem to think
that I/O contention is a serious problem, such as Stephen
Worthington's "All it takes is one moment when the
disk is too busy and you will lose a block of data and seconds of one
or more recording."?  That just doesn't seem to be the case.

So far, the only sensible reason to prefer 2x1TB drives over 1x2TB
drives is "I have a couple of 1TB drives I can recycle".

Eric


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