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Stress Testing MythTV Backend

Posted 04-15-2011 at 02:14 AM by disturbed1

My cable provider, WOW!, is starting their digital migration. Lucky for us, they've decided to listen to the customers, and are broadcasting their digital stations on Clear QAM!!!!

This digital migration means that I have to add/replace/upgrade some tuners in the backend. I'm currently running with 3 analog tuners (Asus Falcon2 x2, plus a HVR1600), and a single ATSC/QAM tuner from the digital side of the HVR1600. WOW! is doing their migration in stages, which means the analog tuners are still of some use for right now. Gives me a chance to try out something new.

While at Microcenter the other day, I decided to pick up an HDHomerun from Silicon dust. I've read more than enough about these devices to know I wanted one. MythTV integration is easy, though the scanning needs some work. Luckily WOW! has told us what channels are on what multiplex. Makes channel editing extremely easy. The HDHR (or is it MythTV?) does not pick up the names for the QAM channels. Where as the HVR1600 does.

Our backend was recently upgraded from a single core Sempron 3000+ (1.8Ghz), to a dual core E8500 (3.16Ghz x 2). Currently only 2 drives for the TV Recording storage group. Samsung 500GiB, and WD 320GiB. There's a 2TiB and a 1TiB drive for movies, music, files, and other stuff. Recorded shows rarely stay on the machine for longer than 2 days. Most of the time, we watch the shows latter the same night they were recorded. We also practice watch and delete.

The HDHR unit I bought was version 3. This thing is small. Slightly bigger than a pack of smokes. Power jack, Ethernet, and a single coax. The tuner is a dual tuner that also supports multi-rec. Means I can theoretically record 4 stations at the same time from a single HDHR. Of multi-rec only works for stations on the same multiplex. For example, WOW! has mapped Speed and Hallmark on the same multiplex (113), MSNBC and Animal Planet are on another multiplex (112). So I can record all 4 of those stations at the same time from this single unit.

Onto the testing -

I decided to queue up a few recordings to test things out. First does multi-rec actually work? Can the HDHR send 2 HD stations? 3? how about 4 HD stations at the same time. I also wanted to see if this e8500 with only 2 SATA drives could handle the data flow, along with the network topology.

For the HDHR, 2 simultamous HD streams were no problem at all. I did run into occasional collisions with 3 HD streams. This resulted in skips, and blocking on the streams. Perhaps if the HDHRs had gigabit NICs instead of 10/100. I could not test 4 HD streams. It wasn't possible with WOWs current multi-plex mapping. Though given the results of the 3 HD streams, I'd guess the results would not be acceptable. Running each tuner with an HD and SD stream (4 recordings, total of 2 SD and 2 HD) were a non issue. The e8500 and SATA drives did not even break a sweat.

Push it a little more -
HDHR - Tuner 1 - 1 SD, 1 HD
HDHR - Tuner 2 - 1 SD, 1 HD
HVR1600 - ATSC/QAM - 1 HD
No problems --- iostat reports 85+% idle

Next step -
HDHR - Tuner 1 - 1 SD, 1 HD
HDHR - Tuner 2 - 1 SD, 1 HD
HVR1600 - ATSC/QAM - 1 HD
HVR1600 - Analog - 1 SD
ASUS #1 - Analog - 1 SD

That's a total of 7 streams being recorded at once. 3 HD streams, and 4 SD streams. iostat never peaked above 40% usage (60% idle) for either HD. Top reported a load average of 0.67!!!

Even when I fired up 3 MythTV Frontends, 2 playing back an HD recordings, and the 3rd watching live TV on the last free tuner, there was not a single hiccup. iostat did hit 60% usage, and the load average went upto 0.85.

I'm truly amazed. This is quite a bit of data floating through MythTV. It's not just a testament to how stable Slackware is, but how stable MythTV actually is. Kudos to the teams involved here.

I plan on adding 2 more HDHRs, removing the 2 Asus Falcon2's, removing the WD 320GiB, and adding 2 more Samsung 500GiB drives. The Asus Falcon2's will be removed, because once WOW! completes their digital transistion, everything will be available in clear QAM. Though they will continue to broadcast 6 local stations, plus a few public access channels. The locals are already broadcast in HD, so there's no real reason to keep the Falcon2's in the loop.
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