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07-02-2017 07:23 AM - edited 07-02-2017 01:35 PM
c7000 Blade Enclosure Power Settings
We have a setup where C7000's are hosted within racks together with other equipments (DL servers or 5930 switches, or 3PAR storage). C7000 redundancy mode is set to N+N.
The racks are powered each over 6 AC lines via 2* AF513 PDU's, each line powering up one PSU of the enclosure + other equipments (in fact in the distribution panel the feeding is 3 phase 380V, but then each phase is connected with the neutral wire RN, or SN, or TN - thus giving 3x 220 V single phase, instead of 380V 3-phase). Each phase is having a 16A fuse in the distribution panel.
Example: ph 1 - A will feed PSU1 of the C7000 + source A of switch1, ph 1- B will feed PSU4 of the C7000 + source B of switch1, etc.
The consumption on each line (phase) is calculated not to over pass 80% of the 16A (branches A+B summed).
(1) Nevertheless, I think 16A per phase is the de-rated value for the AF513 PDU, so I wonder if we should have used 20A fuses in the distribution panel?
(2) This calculation assumes that power supplies of the C7000 draw current equally and fairly balanced. To my understanding this means that Dynamic power saving mode shall be set to disabled.
Is this applicable when AC lines on the branch B, let's say, are all failing? That is, if all the power in the enclosure is provided via PSU1, PSU2 and PSU3 (in an emergency situation) will the principle of equally sharing the load among the power supplies be valid? ("When Dynamic Power Savings mode is disabled, all power supplies share the load equally." , <Managing HP bladesystem c-class systems>, technology brief, 2nd edition).
- one c7000 with 14 blades is estimated to draw at max load ~25A.
To be able to observe 16A * 80% limit for each AC line we need to be sure that via each PSU it will draw not more than ~25A/3 (that is, summed up with the other equipments not to over pass 12.8A).
(3) Could Enclosure Dynamic Power Capping (e.g., Rated Circuit Capacity) feature be useful in this situation?
Thanks a lot in advance!
08-27-2017 12:03 AM
Re: c7000 Blade Enclosure Power Settings
1) Yes, I would have put at least 20A Breakers in. My Chassis are powered via a 30A PDU on a 30A Breaker, though its admittedly a bit overkill. 20A is a pretty safe bet to stick with. Last thing you need is to trip your breakers whenever your servers go under load.
If you take the Power Backplane out on the 3 phase units and take it apart (This may blow your warranty so you may just have to take my word for it), the two lines are attached to 3 of the PSUs each.
Line A connects to PSU 1, 2, 3 and Line B connects to PSU 4, 5, 6
All the 3 Phase Backplane does, is hook up the first phase and common to 1, 2nd phase and common to 2, 3rd phase and common to 3., and the same idea for Line B and 4, 5, 6. There literally is no electronics or regulation circuitry etc built into the backplane. Just a direct wire to each PSU. This gives each 120V phase to the PSUs. (Also why a Phase Emulator will only replicate 2/3 phases, and subsequently only power 2/3 PSUs). The PSUs are able to handle both Single and 3 Phase.
2) I dont know the answer to this
3) Yes, to prevent tripping your breaker. HOWEVER, know that you will be capping and restricting your Blade's performance and it may not be able to ramp up to the expected speeds to do its job efficiently. Its much better to put the proper breakers in the first place.