MDS 9513 and AC power connections

Each Power Supply have two AC connections for redundancy, it will be better if you connect both of them to separate PDUs, just in case if one of them fails.

You need to connect one to PDU 1 and the other to PDU 2 to avoid a single-point-of-failure.

I think it is the 2 power supplies that give you the redundancy not the 2 connections to a single power supply. Check out this from the Hardware Installation Guide:

One AC power connection @110 VAC = No output

Two AC power connection @110 VAC = 2900 W output

One AC power connection @ 220 VAC = 2900 W output

One AC power connection @110 VAC and one AC power connection @ 220 VAC = 2900 W output

Two AC power connection @ 220 VAC = 6000 W output

Another note, not a power guy here, but any need to be worried about what phase you are connected to? Assuming you have multiple phases in your DC.

Hmm..so your advices is different from the other guys. You recommend which config:

config 1:

config 2:

so in case one PDU fails, it's better to run with both power supplies in "degraded" mode versus one power supply in "optimal"mode and one completely dead ?

Here is the text below the slide I got that picture from:

"The figure illustrates an incorrect and correct connections sequence to external power distribution units. When configured in redundant mode (default), the wrong connection sequence can leave the switch with only 2900W, which can result in the chassis shutting down line card modules. This would require manual configuration to set combined mode, upon which 5800W power capacity is available. There is no automatic provision to configure combined mode in the event there's a loss of an external power source.

The correct connection sequence provides the full 6000W capacity in the event an external power source fails."

so if two AC power connection at 220 give me 6000W, but one AC Power connection at 220 only gives me 2900.

So if i have PDU die on me, i am left with two power supplied, each running with one power connection. So each is giving me 2900 for a total of 5800 W, but is not equal to 6000W.  Am i completely off with my calculations ?

You'll need to determine how much Watts you need for your switch. Let's assume you need 5500W to run all your modules. You would connect 2x220V to each power supply (4 power cables connecting to the chassis), this would give you a total of 6000W available. You would setup your power on the MDS as redundant, which is best practice. So if you lose a whole power supply, the other one as able to keep the entire chassis powered up.

I don't think you would want the power supplies connected to different PDUs in this scenero because if PDU goes bad both power supplies would be knocked down to 2900 W which couldn't power all your modules. Now if you had each power supply connected to it's own PDU you could lose a PDU or power supply and keep everything powered up.

I recommend config 1 and actually those pictures just reminded me of something. I pulled out my book from the Implementing Cisco Storage Networking class and here is the picture in it (sorry for the quality took it from my phone):

I agree with your suggestion of connecting the power connections with the same PDUs. However would like to make a note here, that in case if you are on single 220 volt supply also the switch would receive the required power:-

Max power requirement = 2622 W to 3050 W (all 528 ports in use).

Power supplied when one 220 Volt connection is there = 220 * 16 = 3520 W {Voltage (in Volts) * Current (in Ampere) = Power (in Watts )}

A 10% variation in this would still remain within the max power requirements.

Thus we can still say that this arrangement also takes care of redundant connection, atleast till the same PDU, though not in all input voltage scenarios.

Thanks for pointing out to connect with the same PDUs.

hersh ..i see the same thing mentioned here:

http://h20000.www2.hp.com/bizsupport/TechSupport/Document.jsp?lang=en&cc=us&taskId=120&prodSeriesId=1849157&prodTypeId=12169&prodSeriesId=1849157&objectID=c00779045

i am going with default config so "config 1" is for me, unless somebody can think of a scenario where "config 2" and "combined mode" on the MDS is more resilient ?

If you have multiple phases of power supply available, I would prefer to use different phases for each PDUs and thus each power supply getting power from a different power phase.

The product data sheet for Cisco MDS 9513, may be referenced at :-

http://www.cisco.com/en/US/prod/collateral/ps4159/ps6409/ps5990/ps6780/product_data_sheet0900aecd80446023.pdf

that would make complete sense to me.

Trey, AbhishekKS  ..do you have any reference material that documents your recommendation ?

I appreciate your assistance guys.