[mythtv-users] Fixed: Choppy watching current recording.

Josh TwoOneSix at thatclothingco.com
Fri Jan 26 18:51:58 UTC 2007

Billy Macdonald wrote:
> Hi,
>     I just setup two HD Homerun devices and was having problems
> watchingrecording in progress.  I was getting prebuffering pauses and
> top was showing 15-25% iowait.
>    I could record four HD shows at once and watch a fifth prerecorded
> HD show and that was fine, it was only watching a recording in
> progress that was bad.  I changed the NFS mount options from a rsize &
> wsize of 32768 to a rsize & wsize of 8192.  This lowered the iowait
> times to around 4%.  Playback of a recording in progress now works.
>    I'm not quite sure why this made the difference as I have the
> network bandwidth since watching a HD recording while four others are
> being recorded shows an iowait of 0% and no problems at all.
> Myth-0.20-fixes.  Maybe the it was the file access in 32k chunks that
> was the problem?
> My frontend and my two hdhomeruns connect to a 1G switch to another 1G
> switch to the backend as attempted to diagram below.
> Frontend -- 1G --
> HDhomerun --100 -- Dlink -- 1G -- Dlink -- 1G -- Backend
> HDhomerun -- 100 --
> I couldn't find much info troubleshooting this but after the fix I
> noticed that 8192 is the suggested value in the setup docs, so I guess
> it's there for a reason.
> Billy
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You know what's funny is that I was posting to the "Jittery playback" 
thread a few nights ago and I discovered that my "jittery playback" 
issue went away after I reconfigured my NFS shares in this EXACT same way:
<mythserver>:/video     /video     nfs     rsize=8192,wsize=8192

Now I don't have the "jittery playback" even on my wireless frontend 
machine anymore! I had initially made that change because I was having 
issues connecting my NFS shares (I discovered that if a sub directory 
you want to share VIA NFS resides on a separate physical disk that you 
have to explicitly share it VIA the /etc/exports file or the directory 
appears to the remote client as empty) I had my /video directory shared 
and thought it would include the /video/dvds directory but since I 
currently map my /video/dvds directory to a Seagate 500GB SATA disk, it 
didn't show up. I beat my head against the wall for 2 days until I 
figured that out. Anywho, when I was reading up on NFS shares they all 
said for optimum NFS performance to set the r/wsize to 8192 (I didn't 
previously have it set at all) I didn't even put the 2 together until I 
read this post and now it all makes sense.

Wow, as many times as I tell people to RTFM I guess I should have taken 
the advice for myself for one. :-)

P.S. I made this message long and winded to try and catch search terms 
of others that might find this post helpful while searching the archives 
for this issue.

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