[mythtv-users] MythTV, seeking ahead / behind, NFS, and bandwidth usage

Blammo[doh] blammo at dohboys.com
Mon Aug 2 01:25:46 EDT 2004


I think it may be a Disk IO problem, when combined with NFS.

However, On the local Backend itself, off local disk, I don't see the same
issue, at all, when seeking forward / backward, etc.

digging into it right now, any ideas, appreciated.



----- Original Message ----- 
From: "Blammo[doh]" <blammo at dohboys.com>
To: "Discussion about mythtv" <mythtv-users at mythtv.org>
Sent: Sunday, August 01, 2004 7:33 PM
Subject: Re: [mythtv-users] MythTV, seeking ahead / behind, NFS,and
bandwidth usage


> Great clarification, zero help.
>
> >From what I can tell, seeking is the "normal" and preferred behavior, and
> assumes it's running from the local HD.
>
> FWIW, "jumping" is no faster. It hit the "jump" button and it sits for
20-30
> seconds maybe longer before coming back 10 minutes ahead of where it was
> before. Something is still IO or configuration  bound.
>
> Thoughts?
>
>
>
> ----- Original Message ----- 
> From: "Isaac Richards" <ijr at po.cwru.edu>
> To: "Discussion about mythtv" <mythtv-users at mythtv.org>
> Sent: Sunday, August 01, 2004 2:16 PM
> Subject: Re: [mythtv-users] MythTV, seeking ahead / behind, NFS,and
> bandwidth usage
>
>
> > On Sunday 01 August 2004 04:40 pm, Blammo[doh] wrote:
> > > Two machines in this cluster, both Athlon XP 2400's, plenty of ram,
both
> > > running KnoppMyth R4V4, one backend with two PVR-250's, and a frontend
> with
> > > Nvidia card hooked together on a 100M cisco switch. /myth mounted over
> NFS
> > > from the backend.
> > >
> > > Problem:
> > >
> > > When seeking forward / backward in MPEG2 streams, from recorded TV, I
> seem
> > > to be running out of ethernet bandwidth. I don't notice this AT ALL in
> the
> > > "Video" section with mplayer, just in the TV section. Anything over
say
> 3X
> > > seems to have diminishing returns. All the way up at 8x or 16x,
checking
> > > the switchports shows about 50 - 60meg of traffic running. The load on
> the
> > > backend seems to be pretty low, as does the load on the front end. It
> just
> > > seems like the frontend isn't getting data fast enough.
> > >
> > > It appears to me, that the frontend has to read the whole file, to
seek
> > > ahead / behind in the file, at 1x, 1.5x 2x etc faster. It doesn't
appear
> to
> > > "seek" or "jump" at all ahead, rather reading the whole thing.
> > >
> > > I'm just wondering if anyone else has run into this, and what they did
> to
> > > fix it. Obviously transcoding to a low bit-rate MPEG4 would help. It
> makes
> > > me wonder whether the front end couldn't be a little smarter about the
> file
> > > reading, take less NFS bandwidth in the process. After all, mplayer
has
> no
> > > trouble skipping ahead, etc.
> > >
> > > Thoughts?
> >
> > You're confusing fast-forwarding (what you are doing) with seeking (what
> you
> > want to be doing).
> >
> > Isaac
> > _______________________________________________
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