Is it just a NAS? What cpu usage do you expect? Because I built a tower server with a fan less psu and a Ryzen 5600g and if the server is mostly idle the cpu fan never turns on and even under full load it's just 30% duty cycle and I can't hear it. That being said a u2 has a lot less passive airflow.
homelab
I am looking into something similar. Sharing some thoughts here.
- Use a low power CPU and a passive cooler
- Or, use mainboard with passively cooled on-board CPU
- Go all-SSD, HDDs need more power, need more cooling and produce noise
- Use a Pico-PSU and an external power supply brick
- Or, use a fan-less PSU
Where are the external drives living? Hard drive make their own noise. Might consider going with solid state if you want silence.
One example of this that’s making the rounds: https://www.asustor.com/en/product/FS67
Those machines have a fan at the bottom of the case.
Your best bet is going to be a 4U chassis. You can get 2U chassis with consumer PSUs, but they are going to be more expensive and very limited in terms of parts that will work. You can easily find 4U chassis that support regular ATX internals with proper mounting holes for the PSU and mobo standoffs.
There are some small SuperMicro servers that use Xeon-D (I think? Very low power Xeons that are passively cooled), but you're pretty vendor locked in with those.
Do not use external drives for this. TrueNAS doesn't support it, and you'll be limiting your speeds to that of the USB bus, which is not nearly as fast. Pointless going SSDs if you are using external drives.
I built an almost fanless PC to run MythTV so that it would be quiet (the PC is behind the TV)... that had several HDDs (mass storage) and a SSD (boot / OS) and it works fine.
I say "almost" because I added a case fan - "just in case" and set it to a slow speed and it's been fine.
My advice: check your thermals... use something to alert you if it gets hot under different loads / seasons.
Is 2u a hard requirement? 4u will have better chances to be compatible with consumer PSUs, will have better heat dissipation, more drive bays. And you can add 120mm fan or larger which can be really quiet.