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Power supply

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  • 1.  Power supply

    Posted 06-29-2020 10:41
    In qfx5100 device, is there a zone to which power entry module belongs to. Can I remove one pem when another pem is in the chassis rack. I am concerned that this mustn't take my device offline. I know most devices have host removable sub parts. But is there a way I can achieve to inter change the pems. At a point while I replace there will be only one pem supporting the box. Is this specific to AC and DC type or sub device type like qfx5100 variants. I am doing this to check issue with pem rack. To note issue with pem rack I have been advised to change pem and note the error sequence. All details or any links can help me in this matter.

  • 2.  RE: Power supply
    Best Answer

    Posted 06-29-2020 10:55

    Hi Reload,


    To answer your queries:


    1) As per my knowledge, there is no zone concept in QFX series devices as seen in MX. One reason why I believe this to be true is, the power supplies are 1+1 redundant. The device is capable of working on a single power supply and there is no load sharing as far as I am aware of.


    2) Yes, you can remove a PEM with the other PEM in its slot (PEMs are hot-insertable and hot-removable). At a given point in time, the chassis should have one healthy PEM inserted in the PEM slot. As mentioned above, the power supplies are 1+1 redundant.



    3) If the device has a working and healthy power supply inserted in one of the PEM slots, the device stays up.


    4) In case you want to inter-change the PEMs in their slots, you can choose to do this one PEM at a time. If you do not want your device to undergo a shutdown, please use a spare third PEM to achieve this seamlessly.


    5) I believe both AC and DC power supplies are 1+ 1 redundancy which makes it, NO. There is no specific AC DC type that will change this rule.

    6) You need not change both the PEMs in slots to check the issue with one PEM. In case there is an issue with both PEMs, the device is taken down in an ideal case.


    The below links might help you with replacements(or even in swap test):






    Hope this helps 🙂


    Please mark "Accepted Solution" if this helps you solve your query. Kudos are always appreciated.

  • 3.  RE: Power supply

    Posted 06-29-2020 10:58



    Power supplies should be redundent to each other not having certain power zones to serve.


    If this solves your problem, please mark this post as "Accepted Solution.

  • 4.  RE: Power supply

    Posted 06-29-2020 20:53

    Hi Reload, 



    • The QFX5100 is shipped from the factory with two power supplies. Each power supply is a hot-removable and hot-insertable field-replaceable unit (FRU) when the second power supply is installed and running
    • You will need an working spare PEM to swap the Power Supplies position. If only one power supply is installed in your QFX5100 device, you need to power off the switch before removing the power supply.

    Verify the status of PEM and also if the PEM airflow direction matches the chassis:


    show chassis hardware | match Power
    show chassis environment | match Power
    show chassis environment pem 


    Verify that the airflow direction on the power supply handle matches the direction of airflow in the chassis. Ensure that each power supply you install in the chassis has the same airflow direction. If you install power supplies with two different airflow directions, Junos OS raises an alarm. If you need to convert the airflow pattern on a chassis, you must change out all the fans and power supplies at one time to use the new direction.


    Reference Links: 

    1. Removing a Power Supply from a QFX5100 Device 
    2. AC Power Supply for a QFX5100 Device 
    3. DC Power Supply in a QFX5100 Device 


    Hope this helps. Smiley Happy


    Please mark "Accept as solution" if this answers your query.  Kudos are appreciated too! 



    Sharat Ainapur


  • 5.  RE: Power supply

    Posted 06-30-2020 10:37

    Hi Reload,


    the QFX will be able to run from one power module, these are hot swapable, as long as you keep one power unit the switch will not go offline.


    Hope it helps,