pre-tuning baseline streaming data run for new JR4s

In the late 80s, right before I finished undergraduate work at Stony Brook, I bought an orange colored 1973 Chevy Nova. It was, well, butt ugly. But it had a 350 small block engine in it which, as I had been told by people (supposedly) more knowledgeable than I (in these areas), was shared by the Corvette models of that year.

I don’t know if that was true. I do know that this was an engine I could tune. But I had to establish a baseline. Which I did (legally). There was a highway near my parents home that had some longish stretches with good entrance ramps. I’d time how long it took me to hit the speed limit (55 at the time) from entering the highway at a constant speed.

The measurement wasn’t perfect, but it was pretty repeatable. Stopwatches are easy to operate with one finger.

What I do remember was, for the baseline tests, punching the accelerator, hearing the cars engine roar, and getting pressed back hard in my seat. The exhaust system had a hole in it somewhere, that I was loathe to fix (allowed lower exit pressure for the cylinders, which improved power from what I was told). You also had to be cognizant of maintaining rolling friction, and not cause the wheels to break friction and spin. If you were able to couple enough power to the wheels, you could do this.

I wondered if I could tune it. Tweaked things. Took measurements. Some stuff helped, some didn’t. I was able to learn how to get more power out of the car.

Why is this relevant to JackRabbit?

Pre-tuning numbers for a new system. I had a distinct impression of being pressed back into my seat.

root@jr4s:~# !146
dd if=/dev/zero of=/data/big.file bs=16M ...
4096+0 records in
4096+0 records out
68719476736 bytes (69 GB) copied, 36.7492 s, <strong>1.9 GB/s</strong>
root@jr4s:~# dd if=/data/big.file of=/dev/null bs=16M  ...
4096+0 records in
4096+0 records out
68719476736 bytes (69 GB) copied, 40.9035 s, <strong>1.7 GB/s</strong>

Thats 1.87GB/s writes, averaging 124.6 MB/s per drive, across 15 data drives. With 1.68GB/s reads, averaging 112 MB/s per drive, across 15 data drives.

This is before tuning, and with the system configured in the detuned mode, specifically to ensure stability.

We have some additional features that could push this higher in this configuration. We may try a different configuration as well. If I am right, we could get an extra 300 MB/s out of that other configuration. Pre-tuning.

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