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BladeSystem - General
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Energy efficiency of additional power supplies in c7000

 
Simon Haslam
Advisor

Energy efficiency of additional power supplies in c7000

Hi

I'm planning a single enclosure c7000 system, initially populated with only 4 blades and a single phase, 240V electrical supply.

I've been using HP's Power Advisor tool to work out the optimal numbers of fans and power supplies. However I have noticed whilst each fan (above the minimum required) adds about 140W load (variable in practice of course), additional power supplies don't make any difference to the estimated consumption.

This is not what I was expecting from experience with other (older) systems - each power supply usually has an overhead, plus multiple active-active supplies will be running at a lower average load, usually reducing efficiency.

As it happens I should be OK with 2 power supplies and 6 fans, though may end up with 3 power supplies as we expand the system.

Is this a limitation in the current version of the Power Advisor tool (rev. 1.46), or does it reflect improvements in the power supplies (Platinum rated)?

Does any one have any measured power data they can share?

TIA!

Simon
7 REPLIES

Re: Energy efficiency of additional power supplies in c7000

>each power supply usually has an overhead, plus multiple active-active supplies will be running at a lower average load, usually reducing efficiency.

I assume because the OA in the blade knows about everything, it can be more efficient in power and cooling.

>or does it reflect improvements in the power supplies

Not just the power supply, the whole OA that can simply turn off unneeded power supplies and run the rest at higher efficiencies.
Simon Haslam
Advisor

Re: Energy efficiency of additional power supplies in c7000

Thank you Dennis - I hadn't thought about the OA shutting down power supplies. We have 6 on order (comes as one SKU) and 10 fans (the HP sales guy obviously did a good job) but as I mentioned we will only need 2/6 so I need to decide how many should be installed (the rest can sit in a cupboard!).

According to the c7000 WW quick specs the 2400W power supply part number is 588603-B21 - I haven't been able to find this on http://www.plugloadsolutions.com/80PlusPowerSuppliesDetail.aspx?id=41&type=2 but I do see a couple of 2450W power supplies which look like blade enclosure ones, e.g. http://www.plugloadsolutions.com/psu_reports/HP_570493-301_2450W_SO-167_Report.pdf, and have 90+% efficiency at >10% load which is impressive.

What I don't understand is why the blade system doesn't have better power efficiency (according to HP's power advisor rev 1.46) when compared to DL380s (all with Platinum supplies):
http://www.veriton.co.uk/roller/fmw/resource/hp_rack_blade_power_100pct.gif
http://www.veriton.co.uk/roller/fmw/resource/hp_rack_blade_power_25pct.gif
Emil Velez
Honored Contributor

Re: Energy efficiency of additional power supplies in c7000

depending on the power mode the power supplies can be in standby mode or the enclosure can draw partial power from all power supplies.

Efficiency is almost the same whether in redundant mode or whether you pull power from all power supplies.

same with the fans.. If you have all of the fans in they run at a lower levelif you have all of them installed.

Simon Haslam
Advisor

Re: Energy efficiency of additional power supplies in c7000

For info:

I've found a section in the OA v3.30 User Guide (page 169) which has an option called Dynamic Power (enabled by default):
"If enabled, Dynamic Power automatically places unused power supplies in standby mode to increase enclosure power supply efficiency, thereby minimizing enclosure power consumption during lower power demand. Increased power demands automatically return standby power supplies to full performance."

I can't find anything about the power efficiency of the fans though. The Power Advisor shows ~140W addition per fan (I'm pretty sure that was across utilisation rates) whereas I expect the consumption will vary according to RPM and the RPM will vary according to measured temperatures (heat produced by components and inlet temp). Therefore maybe having 10 fans installed, even though the enclosure could manage with 6 fans (as it's only part populated), won't use significantly more power. That's one to test though...
David Claypool
Honored Contributor

Re: Energy efficiency of additional power supplies in c7000

Simon, regarding the fans: more fans operating at a lower RPM actually can move more air and consume less power. Your 10-fan configuration will be optimal from a power consumption perspective.
Simon Haslam
Advisor

Re: Energy efficiency of additional power supplies in c7000

That's good news David... but, being the picky type that I am, is there anywhere where this is written down? I don't mean just marketing blurb: "blades are more power efficient" (curiously the Power Advisor tool doesn't really agree) but somewhere where there are some test results/comparisons. HP engineering, or someone with lots of blade enclosures, must have done these tests.
David Claypool
Honored Contributor

Re: Energy efficiency of additional power supplies in c7000

Simon, not possible. Each fan has (IIRC) 64 possible speeds, so 10^64 possibilities, as they all operate independently depending on the amount of cooling required. The Power Advisor will work out your maximums for power circuit sizing, but actual consumption will depend on workload, blade configurations (1 x 80w processor with 2 x 10K drives generates a lot less heat than 2 x 120w processors with 2 x 15K drives) and blade quantities, ambient temperatures, individual blade and enclosure power settings (dynamic power capping, etc).