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xnsub = extranonce subscription. The very very short discription is this feature provides a more stable connection to the Nicehash stratum servers.

P.S. Keep an eye on the ASIC setup page on the Nicehash website as they provide updates if your Antminer requires a firmware or patch update. https://www.nicehash.com/asic-mining (via this link scroll down to ASIC tips & Tricks)

I have over clocked my L3+ to 605 mh/s and can you over clock the S9's ?

To confirm you can overclock the S9. As an FYI any Antminer device that is overclocked instantly voids the warranty

Just a heads up... If you don't keep that cool... You'll brick that L3+

Don't push much past the 400-410 Freq range...

I may or may not have done that by accident with an L3+ ... Don't ask - it was stupid.

On my L3+ I'm running at 444 (580Mh\s) and the fan is set at 60%. My Antminers are in a server room and temps range from 47 to 53 degrees celsius. I didnt overclock my D3 miners as they are running at 17500Mh\s with default settings but I did set the fan at 70%.

Thank you, BTC sent.

Greatly appreciated :)