Important note that the power supply and the fan should have the same air flow
Caution You must order all fan modules and power supplies in the same chassis so that they have the same direction of airflow with coolant air entering the chassis from the cold aisle and exhausting to the hot aisle
You need to buy new fans and power supplies.
I just got mine in today and am trying to decide when to do it. Is it possible to swap one fan module, wait a second to make sure it turned on, then swap the other fan module? Same process with the power supplies? My concern is it not taking the first new fan or power supply since it's backwards to the to other.
To put is simply, does changing airflow direction require a shutdown?
I just completed the change of airflow direction for Nexus 5548UP while the switch is still online and running. It is possible to swap fan and power modules without shutting down the switch. There are few catches that you need to pay attentions when you want to change the airflow directions:
To swap two fans and two power modules on Nexus 5548UP while it's running:
1) make sure you have the latest IOS or at least 6.0+, I have system: version 6.0(2)N2(1). Also, please don't forget to save running config just in case if the switch will be shutdown.
2) make sure you have all your new fans and power modules unpacked and ready to be installed
3) connect to the switch console port to monitor the logs and status
4) Pay attention to the switch console, it will give out warnings about fan failure (but switch will continue to run).
5) Important: The first new fan that you just replaced (with opposite airflow direction), the switch will detect the the incorrect airflow, and begin to give out warnings with countdown timer. You have only less than 60 seconds to complete the rest of swapping before the switch will shutdown. Not only you need to swap out each module quickly, but need to pay attention to each new module wait for it online before replacing the next module.
6) To start the process, insert in the first new fan with opposite airflow direction, take about few seconds and wait for spinning up [green light]. The switch console will display: "incorrect airflow detected, the switch will shutdown in 60 seconds.....". Just move onto next step...
7) replace the second fan, wait few seconds for new fan to spin up [green light].
8) replace the first power module
9) Important: make sure the first new power module is online [green light], then you can proceed and replace the second power module.
10) Completed! you may check "show inventory" to see if all new fans and power modules are online and shown. The switch was up and running the whole time.
Please give rating if it helps you! Thanks!
Luckily we have redundant Nexus switches. As reported in this post after you replace the first fan the switch console goes into a 60 second shutdown timer. The first switch I swapped the fans and power supplies I was nowhere close to getting them swapped out within the 60 seconds. The switch shutdown and I had to pull power to both power supplies and reboot it. No harm done, but I was hoping to avoid having to reboot the switch.
I had high hopes on the second switch and had all my fans and power supplies right next to the switch, took off my coat and moved as fast as I could. I managed to get all the modules replaced with 5 seconds to spare, but I guess the 5 seconds remaining wasn't enough for the switch to realize all fans were in the correct airflow direction and the switch shutdown.
Bottom line, unless you can get two people to swap components on the fly or are really, really fast, plan on a switch outage.
As to the previous information above from Rocky Cheung, I am currently doing a project in which we ran into this problem. 8 of our switches had IOS 6.0 and above, while 2 of our switches had an IOS lower than 6.0. When we tried to put in the reverse flow fans and power supplies, the switch with the lower IOS below 6.0 read the fans as a mismatch, and the switches shut down completely. Luckily we have redundant switches, so no traffic was lost.
Before you start this, please check with Cisco to make sure that all of your switches that you plan on doing a power supply and fan upgrade switch have the IOS at 6.0 or higher (preferably at the latest IOS possible), otherwise the switches will fail.
Also, please note that you have to be fairly quick with this, and I would say have all of your parts laid out very close to your switch so you can get this done in less than 45 seconds. Anything longer, and the switch will shut down and you have to wait for it to reboot.
And please note that this is NOT the way Cisco recommends doing this. They do recommend that you shut down everything, then replace your fans and power supplies, and then have it boot up normally. But again, the most important thing is to make sure your IOS is updated past 6.0. We just tried doing this the recommended Cisco way and the new fans and power supply was not recognized, so upgrading the IOS is vital for this to be successful.