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Chassis fan redundancy question

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Chassis fan redundancy question

Rick wanted more info on chassis fan redundancy:



In a fully populated enclosure. 16 blades.


Regarding the fans within the C7000, I'm aware of the "fan zones" but not sure how many fans I need per zone (I'm also aware that fans 3 and 8 straddle fan zones). How resilient are the fans within a zone. If I lose Fan 4 and 5 in Zone 1, Will the blades stay up and running because Fan 3 is still running ? What happens if all 3 were to fail (3,4,5). Would Zone 1 blades shut down ?



Monty went into depth on this one:



There are four fan configurations supported in c7000 as shown in the c7000 Enclosure Installation and Service Guide section:


Installing fans

The HP BladeSystem c7000 Enclosure ships with four HP Active Cool 200 Fans and supports up to 10

fans. Install fans in even-numbered groups, based on the total number of blades installed in the enclosure.

• Four fan configuration—Fan bays 4, 5, 9, and 10 are used to support a maximum of two devices

located in device bays 1, 2, 9, or 10. Only two device bays can be used with four fans.

• Six fan configuration—Fan bays 3, 4, 5, 8, 9, and 10 are used to support devices in device bays 1,

2, 3, 4, 9, 10, 11, or 12.

• Eight fan configuration—Fan bays 1, 2, 4, 5, 6, 7, 9, and 10 are used to support devices in all

device bays.

• Ten fan configuration—All fan bays are used to support devices in all device bays.

• Install fan blanks in any unused fan bays.


  • 4-fan rule – supports maximum of two Devices in bays 1,2,9 or 10
  •       Wanted=4, Needed=3
  • 6-fan rule – supports max of eight Devices in bays 1,2,3,4,9,10,11,12
  •     Wanted=6, Needed=5
    • 8-fan rule – supports all Device bays
    •     Wanted=8, Needed=7
      • 10-fan rule – supports all Device bays
      •     Wanted=10, Needed=9


The four zones in the c-Class enclosure are cooled by the fans directly behind those zones (with a little bit of help available from other zones). There are at most 2 ½ fans in each zone.


If you examine the 4-fan, 6-fan and 8-fan rules, you will see that if a single fan fails – that zone only has one fan to cool the devices in that zone.  One more fan failure could result in no fans to cool devices in that zone.  This is why the cooling is only N+1 redundant.


Wanted fans for a fan rule achieve N+1 redundancy.  

Failure of a Wanted fan will result in the loss of redundancy in the fan subsystem for the 4-fan, 6-fan and 8-fan rules.

Failure of a Wanted fan in 10-fan rule results in the OA automatically reducing to the 8-fan rule – and if the fan that failed was either fan 3 or fan 8 which are not Needed in the 8-fan rule, the fan subsystem continues to be redundant since all eight wanted fans are still operational.


Needed fans have no redundancy – one more fan failure will likely result in the zone that has no fans left.


This is Thermal Logic which does not require any user configuration, permits minimal enclosure fan configurations and protects against single fan failures.


I hope this helps.



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