Total power of redundant PSU

I

Iron67

n00b
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Oct 4, 2008
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Hi,
I have this chassis http://www.supermicro.nl/products/chassis/4U/846/SC846XE26-R1K28.cfm?parts=SHOW

It is equipped with two redundant PSUs and a power distibutor with four slots. Two occupied by the PSUs and two others free for any battery backup power. In the latter it is possible to install additional PSUs.
The power distrubutor has 6*8pin EPS receptacles, 13*4pin ATA receptacles and 8*8pin EPS headers. At maximum current the PDB should transfer a theoretical power of over 4400W.

I have some questions to ask you:
1. Given that the load is distributed on two PSUs, what happens if the total load exceeds that allowed by a single PSU?
2. Is it possible to configure a redundant N+1 PSU system?
 
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So, I'm just going to guess here - I don't have one of these chassis and haven't been able to find any literature that describes it in detail.

1. I haven't been able to find anything that describes the load as 'distributed on two PSUs'. Everywhere I see it discussed, the CPUs are simply described as being 'redundant' which is not the same thing. Most servers with redundant power supplies do not distribute the load, since if a single supply cannot handle the load it violates the descriptor of redundant. I would assume that if the load exceeds the single PSU that you would experience a failure event of some kind.
2. If the answer to #1 is that the active load is limited to a single PSU, then the inclusion of just two PSUs is N+1. You can use the other bays to add battery or other power supplies to move your way to N+2 or N+3, but I think N itself is fixed at 1.
 
I haven't worked with the single server Supermicro chassis. But the Supermicro blade server chassis I have experience with, have 4 power supplies and there you can configure the redundance setup in the rack manager. And it won't let you configure a redundancy setup that leaves you with less power than your currently configured max value. So with 10 blades installed and powered on you may be able to configure N+2 with 4 psus installed. Pull out a few blades and you can actually set N+3 since the total load is less than one psu delivers. But fill up all 10 blades with ram and drives and you may only be able to choose N+1 due to a higher calculated load.

I would assume this chassis works similarly. But I can't say for sure.
 
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