In my last post, "By the Numbers", I talked about the Diversity Factor, and why it is important to know your real one. The DF is in turn based off your "NamePlate" power rating. I talked a little about this, but I think it is worth a deeper dive, as while it is straightforward most of the time, it is not always. Getting this wrong can be a disaster either in a new Green data center design, or in the case of moving something to a Co-Lo, having to go back and re-adjust the parameters of your contract at a disadvantage.


The Nameplate is a label attached somewhere on the power supply. It may not be visible from the back, and you may not be easily able to pull out the power supply to find it. Most computers have just one kind of power supply per model, but there can be sub-models and variations that mess with any assumptions you might make here. I have even seen in some recent models there being two listed power supply models, with one of the power supplies being intended as being more power efficient, and supporting things like taking the server into powered off states during times of inactivity, but being able to be powered back up without a command from a KVM or remote control or even someone standing there and pushing the button. Rather, it powers up as software determines that load in the cluster is increasing, and the servers RAM and CPU need to get on duty.


I also noted in my last post that most power supplies today are "World" power. They can deal with 50 or 60 hertz A/C, and voltages ranging from 100 through 250, all without giving you blue smoke. In the technical world, it is considered bad to let the blue smoke out of the computer, because you can never get it back inside. That same auto-ranging capability means that you have to know the wattage of the power supply by explicit vendor statement. It has to say something somewhere about 1100 watts or 2000 watts or whatever. Volts times Amps does not get you there.


So what if there is no nameplate, or if there is no easy way to get at the nameplate because the server is powered up and the users would be grumpy about you powering it down to find the nameplate?


Also, what if you can see the nameplate, but the server has more than one power supply? Is it active active? N+1 N*2? Active / passive? No way to tell from the Nameplate.


The Google is of course your friend.


Searching the Vendor Sites


Some Vendors are better than others about keeping the data about their computers online. Others are very aggressive about removing data that is on older systems that they have discontinued. Kudos here go to Sun (pre Oracle: I am watching to see if they maintain this level of goodness) and special mention to Dell. IBM is a problem for really old systems, and because things can be spread out quite a bit, and because they use the word "Power" in their server names, leading to many false trails. HP's and therefore Compaq and Digitals doc is very good. Or very bad. Or very missing, depending on what you are looking for. Cisco is pretty good, though the different generations are documented in different places of different docs.

Some old stuff is just not findable.


When trying to find out something like nameplate wattage, these keywords in various combinations are what I have found the most useful:


  • Model Name (like Enterprise 250 or 7015-r40)
  • The vendor name
  • watts
  • power (except for IBM where this is nearly useless)
  • specification / specs / "technical specification"
  • "power supply"
  • Searching used computer depots for replacement power supplies
  • Maximum BTU


About that last one: You can reverse into wattage from BTU. Make sure you use the Maximum BTU rating to keep everything in Maximum Wattage until you apply the DF. You only want to apply the DF once, and to the right number.


Wattage from BTU is 3.414 BTU's per Watt. 680 Maximum BTU's in a specification sheet means the maximum wattage of that power supply is 200 watts.


Again: Maximum rating. Keep it all the same. Some vendors will give you an estimate of the median power usage, and they may give it in watts or BTU's. Doesn't matter. They have no idea what your config is, or how it fits into your overall data center, and what your measured diversity factor is. Might be handy to know for figuring out potential hotspots if it looks like the median is close to the max. But track it separately and do not confuse them.




BMC's ADDM is another way to find out the nameplate of your servers, and to do it in an automated fashion. I have recently learned how to do some very basic things with ADDM, and the part of this that I really need for designing and maintaining my R&D data centers is this: ADDM can not only discover everything on my network, but it has a database (called the HRD, or Hardware Reference Data) of servers and other gear, with over 1,000 entries, that can enter into the CMDB not only all the other information about the server (OS, patch level, disk config, network config, etc), but update the MaxPower entry in the Atrium CMDB with a servers Max watts rating. Then it is a simple matter of pulling the data out of the CMDB by rack, row, room, or whatever, and having your max wattage right there.


In addition to wattage, you have to know the servers size to figure out rack configuration, in Rack Units, or EIA U. ADDM's database has that too, and can populate the CMDB with that as well.


This is only the tip if the ADDM iceberg of course. It does way more than just populate power and system size in the CMDB.


In combination with the diversity factor, you now have everything you need to figure out how you want to set up the servers in new configurations and densities.