[mythtv-users] Odd i/o issues

[John Finlay]

Michael D. O'Brien wrote:
> In the last week I've upgraded my back and frontends to Ubuntu 8.10 
> and the newest myth-fixes.  Last night, I noticed that the show I was 
> viewing was pausing every few seconds, rendering it nearly 
> unwatchable.  I knew the backend was recording a few other shows and 
> the frontends hadn't shown this behavior while the backend was idle 
> earlier that day, so I did some looking around:
>
> -top on the backend and frontend showed plently of available memory 
> and idle cpu
> -it's not a network issue, the maximum usage in iftop on the frontend 
> looked to be about 12mbps (out of 100) and on the backend around 
> 30mbps (out of 1000), due to recording 2 shows off our hdhomerun while 
> I was watching this other show.
> -on the backend, top shows iowait hovering around 20-40%, which isn't 
> bad and was common while recording 3 HD shows and watching 1
> -on the backend, iostat -xk 1 shows something interesting: my raid5 
> array participants are all being used, but it seems that two of the 
> drives hover around 10% usage, while one is constantly pegged at 100% 
> usage.  Is this normal behavior in iostat -xk for a raid5 array?  it 
> seems odd to me.
>
> My backend is a C2D e6320 with 3GB of ram running Ubuntu 8.10 and the 
> newest myth-fixes.  Myth records to a raid5 array of 3x750gb drives 
> with a 1.5tb xfs file system on top.  It's connected to the network 
> via 1000bT ethernet.
>
> My frontends are AMD x2 4000+ with 1GB of ram running Ubuntu 8.10 and 
> the newest myth-fixes.  They are connected to the network via 100bTX 
> ethernet.
>
> Thoughts?  I'm intrigued by the what seems to be strange iostat 
> results on the backend...
I have experienced similar pauses (though not as often as you) in my 
system as well since upgrading the kernel (to 2.6.24-23) in my BE which 
is running mythbuntu 8.04.1. I can't for sure say that the kernel is the 
problem but I am suspicious since I noticed the problem shortly thereafter.

John