Lets start from basics. If we want to replace something, first we should know what are we actually replacing.
I have no idea if it's good or bad but it's 12V so I got 12V version of A4x20 PWM Unfortunately it's not as straightforward as slapping new fans and calling it a day. Screw holes in CRS317 are too small for rubber mounts so I had to mount them from the other side than standard. Due to small size of fans and really long rubber mounts I had to cut them:
Unfortunately it's just beginning of issues. It turns out fans don't start up between 40 and 50 degrees on CPU and slightly "kick" trying to spin up. Without success:
I set up small lab to figure out whether they will eventually spin up (laptop blowing hot air on CRS317 heatsink):
And yeah they do, after reaching 50 degrees on CPU. Which is not that bad but it's something to keep in mind. I found this thread bringing up similar topic:
While it's no longer true (fans do spin up properly during initial startup), it's still somewhat relevant. Also yeah, it'd be nice if those options in CLI actually worked because as of now - they still don't do anything. Problems don't end here though. NF A4x20 seems to push significantly less air than stock fans and provides waaaaaaay less static pressure. It made me a bit worried about cooling of unit, especially considering far from perfect placement in desk so I soldered and assembled custom small fans controller hooked up to adjustable 3-12V power supply:
So final setup looks more or less like this:
Comparison of temperatures before and after goes like this:
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[lapsio@CRS317SWAG] > /system health print temperature: 48C cpu-temperature: 37C psu1-state: ok psu2-state: fail fan1-speed: 4080RPM fan2-speed: 3915RPM
So... how's aftermath? Well, switch has higher temperatures because there's inferior airflow, due to additional 120mm fans is not all that much quieter, warranty is voided, money spent on fans. That was nice day
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[lapsio@CRS317SWAG] /system health> print temperature: 51C cpu-temperature: 40C psu1-state: ok psu2-state: fail fan1-speed: 4935RPM fan2-speed: 5010RPM
All in all - if you have CRS317 as home switch for lab or something then maybe? It's somewhat worth it? But for any even remotely production-like use big nope.