[mythtv-users] System Load/Performance Question

[Michael T. Dean]

On 02/19/2006 05:20 PM, Brian Wood wrote:
> I know the "can this system do <blank> has been done to death here,  
> but I need some comparisons.
>
> The system is an amd64 3700, running Gentoo 2.6.15, MythTV  
> 0.18.1,1.5GB RAM
>
> We are talking strictly about SDTV here.
> 2-PVR-150s
> GeForce-5700 video card w/256MB.
> nVidia 7676 drivers, no XvMC, MythTV compiled with OpenGL support
>
> Recordings are going onto 2-250GB SATA drives configured Linux kernel  
> software RAID0, JFS filesystem.
> Ring Buffer is going onto a UDMA 133 250GB single drive, JFS  
> filesystem, no other drive on the IDE channel, The OS is on another  
> partition of this drive.
>
> If I have a recording happening on tuner 1, and am watching LiveTV  
> from tuner 2, and have a commercial flagging job happening, I get  
> digital breakup on the live picture, and occasional breakup in the  
> recording.
>
> Without a flagging job running there is no breakup on liveTV or the  
> recording.
>
> CPU usage shows about 30-35%, no swapping is happening.
> The priority of the flagging job in MythSetup is set to "low".
> vmstat shows "WA" as "1", and very occasionally "2"
>
> So, my questions:
>
> Is this normal, am I simply asking too much of the system?
> Is it a disk IO problem? (I don't think it's a CPU problem)
> Would putting the ringbuffer on the RAID system help?
> Would moving to a SCSI disk system help?
> Should I just run flagging jobs at other times?
> Is having the ringbuffer on the same drive as the OS a bad idea?
>
> Obviously I'd like to figure out what the weak link is in this system  
> that is causing the breakup, any ideas appreciated.
>   
Doesn't really answer your question except to say that something's 
messed up, but I've recorded 4 different shows via 4 PVR-250's with one 
"near-real-time" mythcommflag job running while watching a 
previously-recorded show on a combined frontend/backend running on an 
AMD Athlon XP 2000+ with 512MB RAM, an NVIDIA GF4MX440 without XvMC, and 
3 UDMA 100 disks on 2 IDE buses in an LVM group (no RAID) using ext3 
without any problems.

Mike