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Design

In this draft design, I'll lay out the rack design and hardware necessary to power dozens of servers.

Bill of Materials

The Rack

Do you need to do 1/2 a cabinet?

No. You could do this smaller.

But for this example, I'll do 1/2 a cabinet with room for things like battery backup / UPS...

  • 1/2 Cabinet: $374.00
  • 6U DIN Rack/Cable Mgmt: $199.00

Total: $574.00

The basic host

The basic host configuration is as follows - PoE Powered Raspberry Pi - NVMe Attached Disk - Vertically mounted on DIN rails - No case required - better airflow and cooling

This ultra low profile design dispenses with the bulky and failure prone PoE HATs. The PoE hats often have fan failures and take up valuable HAT space for other things. The carrier board in this BOM has the NVMe on the bottom of the board. With this design, the disk and PoE do not take up any HAT space and also don't glog up the rack with USB cables. The NVMe is also attached with PCIe speed rather than USB.

Cost - NVMe (512G): 69$ - Raspberry Pi 4 (8G): 75$ - Waveshare Carrier Board: 30$ - DIN Mount: 15$ - Network Port (Switch / Num Ports): $ 11.45 per port (1) - POE Splitter: 20$

Total: $221.00 / node

Could you get used gear for this cheap? Yes. Would it be more powerful? Yes. But... - It's bulky as hell (rackmount or old desktop) - Power hungry - Is not expandible - Doesn't grow past the built in number of SATA ports

Density

With the above BOM (Bill of Materials) we'll be able to get roughly 18 servers in to 6U. This assumes 2" width per server. If you choose to go with SSD instead of NVMe, it can be cheaper, but you'll need additional DIN mounts and it takes up more rack space. Also add on the cost of the USB cables.

Basically you'd need a 24port switch for every 6U.

So in 7U, you'd have the switch, and 18 servers, with cable management.

In that 22U cabinet, you could fit 54 servers.... now we're talking.

UPS

Rack Mounted DIY Battery Packs

Yes, we're going that deep. If you want to of course.

Building batteries from old laptop and car cells is a way to learn how do design power capacity for your datacenter. This is important information if you ever need to design or scope out a cage at a datacenter. Building batteries is also just fun. You can get really creative here with batteries and use all kinds of cells. My personal interest is in batteries that won't catch fire or explode. I'd also prefer batteries that don't off-gas in my office/microdatacenter space.

If you're not familiar with battery types, it's a great time to learn the difference. My personal favorite is Lithium-titanate batteries. These are used in things like weather stations where they are not accessible and have very high recharge cycles. They're basically 20+ year batteries. Their power density isn't as high, but they're safe and won't explode and have a much larger temperature range than typical lithium batteries. LiFePO4 are also safe batteries for this kind of thing.