After running 20 DualMiner 2 units for about 12 hours, I've seen a total of 46 hardware errors as reported by mineninja. The errors are roughly distributed across the units. Only one of them had no errors.
Is this a normal error rate?
Note that I've got fans blowing over the units so I doubt this is a heat problem.
When I grep'd the log, the errors are all like the following example:
[2014-03-10 19:17:25] DM11: invalid nonce - HW error
Note that when I count the error lines from the grep of the log, it shows twice as many hardware errors as reported by mineninja. Maybe cwminer double outputs the errors? I'm not clear which error total is more accurate.
In case it's relevant, I am running with the following command line because I wanted to try to increase the hash rate: --dualminer-pll 850
Should I stop using that frequency option? I don't see an appreciable increase in hash rate anyway. I'm seeing an average of around 66.5 KHs across the units currently.
I would remove the -pll 850 parameter. I am getting appropriate hashrate without using the -dualminer-pll parameter, and I have noticed instability when using this parameter on previous versions of cgminer. Regarding your invalid nonce error, I get those too occasionally, though you should see less once you drop your pll parameter. Are you mining over a wifi connection? This would be the next thing I investigate if removing the non-necessary parameters doesn't help and you are using 9 DMs per p10-u2.