MRV : Why do I get the warning: “VCC too low Warning” on all ports in Slot 1 ?

Doc ID    KNI15142
Version:    1.0
Status:    Published
Published date:    11/08/2017


When I connect I get the warning: “VCC too low Warning” on all ports in Slot 1 


  • MRV


Looking at the logs output you will found that:
Low: Alarm/Warn High: Warn/Alarm 

VCC: (L: 2.900/ 3.000) (H: 3.600/ 3.700)

Now that we know that less than 3.0 but above 2.9 gives us "warning" traps let's look at the slot 1:

Port DDiags Temp(C) Supply(V)
====== ======= ======= 
1.1.1 Warning 36 2.988 
1.1.2 Warning 36 2.983 
1.1.3 Warning 36 2.98 
1.1.4 Warning 37 2.98 
1.1.5 Warning 38 2.984 
1.1.6 Warning 38 2.99
1.1.7 Warning 36 2.988 
1.1.8 Warning 39 2.988 
1.1.9 Warning 37 2.984 

It appears that you are just barely in the "warning" category. This means you may be over the power budget by just 1 or 2 SFP's. If there are any SFP's that are installed but not being used I would recommend removing them from the MCC (or at least unseat them) as they are using power that the operational units need. 

The 8-Slot chassis only needs 2 power supplies. 


Root Cause

From the MCC documentation we have learned that the 3610GMR card has a maximum power budget of 66 watts. We know that the SFP's have to at minimum operate at 3 watts each meaning each 3610GMR card can power 22 of these particular SFP's at any given time. Going through the outputs we can see that you have all 36 ports on slot 1 populated with SFP's all running around 3 watts totaling 108 watts. Going further, it appears that all ports on all cards are full so we will assume 8*108 watts = 864 watts. We then need to add the chassis manager power which the manual states is 320 watts (see snippet). You have a total wattage use of 1184 watts which is 144 watts over their maximum power output. 

And that summarizes the root cause of your trouble. You are oversubscribing power by fully populating all cards. We ask that you unseat SFP's that are not in use to conserve power. We also assume that adding those 2 extra power supplies may have masked the over subscribing problem but you are still running outside of the specifications at this time.

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