Wednesday, January 25, 2012

Hot Hot Hot FEX Fix!

Cisco Nexus 2xxx units run hot in a typical server cabinet because their short depth causes them to ingest hot air produced by servers. Exhaustive (get it?) detail here.

Until now, the best fix has been the Panduit CDE2 inlet duct for Neuxs 2000 and Catalyst 4948E:

The CDE2 works great, but has some downsides:
  • Street price according to a google shopping search is around US $400.
  • It doubles the space required for installing a FEX.
  • Post-deployment installation of the CDE2 will be disruptive - it can't be retrofitted.
Today I learned that Cisco has released their own fix for the N2K's airflow woes. The NXA-AIRFLOW-SLV= "Nexus Airflow Extension Sleeve" is currently orderable, and it lists for only $150!

I've never seen one of these buggers, but I've heard that it's only 1RU, which is nice. I don't have any other detail about it.

I hope that it will be simple to retrofit onto currently installed Fabric Extenders.

UPDATE 2/1/2012 I have some additional information about the NXA-AIRFLOW-SLV.

It's orderable, but the lead times tool indicates that it's on New Product Hold. Cisco tells me that the sleeve will have full documentation and will make an appearance in the dynamic configuration tool (as an N2K option) within a couple of weeks.

In the mean time, there's this: Temperature-Solutions-note.pdf

That document includes the following pictures of the implementation:
Duct with airflow sketch

Installation drawing

FEX with duct installed

Installing this bugger onto an existing FEX (especially one with servers mounted immediately above and below) will be an interesting exercise in problem solving, but looks possible. Power supply cables will need to be threaded through the duct before it's put into place. I wonder if the 2m power cords will be able to reach from the FEX, around the cold-side rack rail, and then all the way to the PDU in the hot aisle?

Also covered in the document is an interesting inlet duct (more of a hat) for reverse airflow FEXen (those with intake on the port end):
Inlet hat for reverse airflow FEX

This guy makes sense if the FEX is mounted flush with the rack rails (as shown above) and has no equipment installed in the space directly above it. It'd probably be easier to mount the FEX so that the intake vent protrudes beyond the mounting rail like this:
FEX standing proud of the rack mounting rail
...But this sort of mounting is usually only possible on the hot side of a cabinet. The cold side is usually pretty close to the cabinet door, and wouldn't tolerate 2" of FEX plus a couple of inches of cable protrusion. This accessory (the hat) doesn't seem to be orderable yet.


  1. Ooooo. I might have to order some of these. This definitely solves a problem for me, ESPECIALLY if they are only 1RU.

  2. Just pinged my Cisco team about this. We'll see what they say. It's so cheap, I might just order one to see what it's really worth in my cabinets. If I get that far, I'll take some pictures, etc.

    1. Pictures? Ha! I'm newly unemployed, so I'm coming over and demanding a tour! :-)

  3. I have received a Cisco document describing the Cisco Sleves. They are only 1 RU.

    1. Cool, can you share that document? If so, please send it along to myfirstname @ mylastname .com


  4. They are not that great. A bit flimsy and they did not provide any holes or notches for the Power cables. This means the cables have to run through the length of the sleeve and come out the front of the rack. Now since PDU's are installed at the back, it means you have to used up 1U underneath it to pass your cables back through the rack. So they are 1U but makes you use 2U because they didn't make any holes to have your power come out. Also if you run containment you'll need to buy some sort of 1U with brush openings so that you can still block most of the air from going through the 1U that your cables need to run through.

  5. I was also surprised to see no cutouts for power cables.

    "since PDU's are installed at the back, it means you have to used up 1U underneath it to pass your cables back through the rack"

    Well, in fairness to the duct, it didn't introduce that particular problem. FEX power cords are going to need to find their way around to the back of the cabinet somehow. The installations I'm familiar with don't require any extra RU. The power cables go through a bristled thing off to the side of the vertical posts in the cabinet.

    Yeah, they're not great, but they're better than nonfunctional, overheated FEXen.

  6. With the discontinuation of Nexus 22xx nd 23xx FEXes, these airflow sleeves have also been discontinued in late 2022. This is shame because they were also sold for the 3048, but the replacement 9k switche for the 3048 and FEXes do not offer a sleeve. We will have to see if they run too hot and need a sleeve... and who offers such a product.