According to Dell's documentation (PDF) administrators can cap the new R720's at a certain Wattage. What are the ramifications of doing this? Will the server power off once it hits the cap? Is there a performance hit to the users accessing the server?
2 Answers
Performance. The feature basically allows you to trade performance for power savings.
It's fundamentally no different than what happens when your laptop or smartphone (etc) goes into power saving mode. The hardware is limited on how much power it can draw, which makes it run slower.
I haven't gotten to play around with that feature yet, so I don't know if you can limit the power to some obscenely low value that would cause the machine to crash/shutdown, but that would not be the intended behavior.
answered Oct 3, 2012 at 19:49
The system can send an alert once the power cap is hit. I believe the Dell implementation will leverage CPU C-States and power P-States to scale back. Why would you have any desire to set a hard-cap?
In my history, I've only done this to allow a group of servers to fit under a power restriction imposed by a co-location facility. Basically, a cap on a single server doesn't make sense, but may be more of an issue with 10-20 systems in a rack, or a blade enclosure, where you may want to keep the aggregate under a particular wattage level.
