jgreco
Resident Grinch
- Joined
- May 29, 2011
- Messages
- 18,680
I thought Avoton TDW is 20W. Are you adding 5w per RAM stick? Also I've heard 5W per HD.
The TDP of a CPU is not what you use. It can be used as a rough guess as to the required watts, but last I looked, there are other parts on the mainboard, and those take power too, and there are fans in the chassis, and those take power too, and there is an IPMI controller, and that takes power too, and there is RAM, and that takes power too, and drives take power too.
Now, if you're building systems professionally, what you do is you actually go to spec sheets and pull the relevant data. A system with 24 sticks of RAM, or high static pressure fans, or dual CPU's, or lots of drives, you have to very carefully calculate the values in order to make sure you're not going to burn out $10K of parts and have to fix that under warranty. You don't go with something "you've heard." I'll be happy to show you a fan that takes 53 watts all on its own. Typically put like four of those in a case and suddenly you've got to budget 250 watts of PSU just for cooling.
But here, we're kind of talking a relatively small system. I took a few liberties and made a few reasonable assumptions based on several decades in the business. You could still do a rigorous analysis, but the thing that swamps a NAS box is drive spinup current, especially with these SoC boards. And the steps between power supply tiers are large enough that even if I was a little off on that 40 watts, or a few watts per drive, it'd fall into the very healthy safety margin I advocated.
That's why I show people the math, rather than just pulling the number they need out of my butt. My number WILL be good, but the reason you should trust it is because I can show you why. In many cases I overestimate a little, because the harm of overestimating is pretty much zero, compared to the cost of catastrophic failure due to underestimating.
But I also took the 200W cue from this setup
http://www.servethehome.com/Server-detail/supermicro-a1sam-2750f-review-matx-avoton-2x-pcie-slots/
Ugh. You don't just pull up some random website, take a random recommendation, then change some of the key parts, and get to think that this has any chance of being vaguely meaningful. Sorry.
A 200W supply is probably just fine for an Avoton with an SSD or a single HDD. It is likely to be woefully undervolting a NAS box with even just four drives, or, if not, then it is probably sacrificing the longevity of components in the power supply.