I brought my second HD5000 (QAM from Comcast cable) tuner online for the first time tonight and set Myth up to record Lost and Amazing race at the same time. And in addition, my PVR500 was recording a show on one tuner and my son was watching liveTV on the other tuner on a different frontend. At about 8:30, I started watching Amazing Race and the performance hit a nasty brick wall.

Playback was horrible, as the recording would pause every few seconds. Once the 2 HD recordings ended at 9pm, everything started playing back beautifully.

CPU on both the Frontend and the Backend systems looked fantastic. My hard drive on the otherhand was getting hammered, obviously writing 2 HD streams from the HD5000 and 2 from the PVR500 and then trying to read the HD stream for one frontend and read an SD stream on the other frontend was just too much for the drive to handle.

I did confirm that I have DMA enabled, that isnt the problem.

Has anyone else pushed their system this hard? Any ideas? I'm thinking of a Raid0 stripe to distribute the disk IO load across multiple spindles might do the trick. Right now my LVM setup is a basic concat and thus all IO tends to go to the first drive until it's filled up.

Would putting the second HD tuner in a slave backend make any difference? They still need to write to the same disk in the end.

Thanks for any ideas.

I say that Raid is the way to go. You could start with Raid 0 but it's risky if you lose a drive then you lose everything.

Brandon gives a lot of good info on his site

http://www.linuxis.us/linux/media/howto ... rives.html

I'd recommed Raid V and use bonnie++ to run a benchmark test

If you can please post your results

My bet is that you have commflag enabled. I run just about as much stuff as you were talking about, and I never have any problems unless an hd program is getting commflagged. Then I have the exact issues you described.

_________________
Have a question search the forum and have a look at the KnoppMythWiki.

Xsecrets

I second that. I have 2 HD cards and dual record and watch with a seperate frontend. I don't have the 500 like you do, but the only time I ever had an issue of choppy was when it was auto set to find commercials. I never search for them now and have had 0 problems.

My backend is a AMD 1900 w/ 2 Air2PC HD5000 cards. Frontend is a AMD 3000.

-duhasst

Mythcommflag has a nasty issue, at least when used with the 'ck' kernel patchset (which I believe Knoppmyth R5D1 kernel chw-8 contains):

It tries to be "nice" by decoding one frame and then sleeping for 10 milliseconds. Unfortunately, this causes the scheduler to raise its priority, usually to above that of the poor hardworking decoder task. So next time it runs, it blocks the decoder task and you get your pause.

Paradoxically, _removing_ the sleep removes the problem. Then mythcommflag appears to the system to be the CPU-hog it is, and it's left at low priority.

From the last post:


How would one go about doing this?

This was discussed previously:
http://mysettopbox.tv/phpBB2/viewtopic.php?t=11706&

My solution was to just change the allowed time to start commflag jobs to when I'm sleeping. (This is done in mythtv-setup).

-Sean

Thanks! I'll give it a try!

Is there anyway to have commflag run only during specific time periods? I would like all my comflagging to run from 1am to 4am, but I don't know how to do this or if it can even be done.

I believe that mythtv-setup lets you select a time window for this under the "General" screens.

tjc is correct. I Just changed the time to allow jobs between 0:00 and 12:00

Cool, I'll have to try this...

Now that I'm recording HD, i'd rather it didn't start commflagging while it's recording another show...