Asset ID:	1-71-1019054.1
Update Date:	2010-07-06
Keywords:

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Solution Type  Technical Instruction Sure

Solution  1019054.1 :   Powering ON the Netra 1290 and Understanding its Standby Power Requirements  


PreviouslyPublishedAs
233881

Description
The standby power budget for the N1290 is such that at least two PSUs must be connected to their power sources simultaneously. One PSU acting alone will not have sufficient standby power to support Fan#3 (which spins on detection of standby power) and will overload after an elapsed time of between four and ten seconds. The PSU will shutdown.

The discussion here will center around the behavior of the standby power of the Netra 1290 server. Standby power is the power supplied to the system by each of four PSUs when they are plugged in to an AC or DC source. This standby power is not controllable by software - it cannot be switched ON or OFF by command, only by action when the power leads are connected or disconnected. This document will focus on the correct timing required to connect each PSU to its power source in order for the system to successfully reach the lom prompt. If the N1290 cannot reach the lom prompt, it cannot be powered ON and so cannot be booted to the OS level.



Steps to Follow
The standby power budget for the N1290 is such that at least two PSUs must be connected to their power sources simultaneously. However, it's possible to connect the first two PSUs in series if both PSUs are connected within about 4 seconds (before Fan#3 reaches full power). In such a case, there is sufficient total standby power from two PSUs acting together to maintain full power to Fan#3 without suffering a PSU overload.

The predecessors to the Netra 1290 (N1280, E2900, V1280) behaved as follows:

    (a)    Connect the first power lead to any one of the four PSUs
            in the server.

    (b)    Fan#3 will spin and reach full speed. All other fans in the
            Fan Tray remain OFF.

    (c)    Connect another power lead to a second PSU. This PSU will
            then add its standby power to that of the first PSU, enough
            standby power to maintain Fan#3 and power ON the System
            Controller (SSC1). The SSC1 will run POST and come to the
            lom prompt.

    (d)    A 'showboards' command at the lom prompt will show all PSUs
            to be in the OFF state (they are currently supplying standby power
            only), and show SSC1 to be in the ON state.

    (e)    Carry on and connect power to the remaining PSUs.


For the N1290 server, the standby power requirement has increased compared to its predecessors. The new Fan Tray comes with more powerful fans and this means that a change is required to the way the power source is connected to the server in order to successfully reach the lom prompt. Occasionally, the following events occur during installation of the N1290...

    (1)    Connect the first power lead to any one of the four PSUs in the
            server.

    (2)    There is a one-second delay before Fan#3 begins to spin.

    (3)    Another 2-3 seconds elapse before the fan reaches full speed
            and draws full power.

    (4)    Four seconds after connection of the power lead, the first PSU,
            acting alone, has its standby power overloaded by Fan#3 and
            shuts down. Fan#3 spins to a halt.

    (5)    The operator is unaware of this and connects the second PSU to
            its power source. But the first PSU has shutdown its standby power
            and so the second PSU is acting alone and it too is overloaded by
            Fan#3 after about 4 seconds.

    (6)    All PSUs are connected to an AC or DC source and the system fails
            to reach the lom prompt. None of the PSUs is supplying power.

A second scenario can occur which makes it appear to an operator that the N1290 does not support N+1 on the PSUs. If there is a delay of more than 4 seconds in inserting the second PSU, the first PSU shuts down. But if the remaining PSUs are connected to a power source in quick succession, the System Controller will run POST on insertion of the third PSU (which is really the second working PSU) making it look like three PSUs are needed to reach the lom prompt.


Solution: 

One possible professional solution is to use cascaded circuit breakers. Each PSU in a pair will have it's own circuit breaker external to the system so that power can be applied to each PSU individually. Both those circuit breakers can be controlled by a master circuit breaker. The master circuit breaker allows power to be applied to a pair of PSUs simultaneously.


Note:

What is N+1 ?
N+1 means that the server has redundancy for an internal power supply failure. That is, a failure on one internal power supply will not bring down the server. To achieve this on the N1290 you need to have at least three power supplies installed.

What is 2N ?
A server with a 2N power system has redundancy for an AC input failure -or- an internal power supply failure, but not both (unless you first lose a PSU connected to an AC source, and then also lose the same AC source). To achieve 2N on the N1290 you need to have all four internal power supplies installed, connected to two separate AC sources.

What is 2(N+1) ?
A server with a 2(N+1) power system has redundancy for an AC input failure -and- an internal power supply failure. This cannot be achieved on the N1290.



Product
Sun Netra 1290 Server

Internal Comments
Filed as Bug 6671430.

The issue described in this document was filed as Bug 6671430. The reason for the bug was to get access to an N1290 so as to reproduce the behavior seen by the customer. Initial testing suggested that PSU0 and PSU1 needed to be the power supplies that should have power applied to them simultaneously. However, further testing proved that any two PSUs were sufficient to provide ample standby power to prevent PSU overload.

N1290 everglades standby power N+1

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