Mainly I felt like building something one day. I live in a tiny apartment, I have no room for a rack of servers nor the associated noise. And I had a stack of random leftover hard drives I didn't have a use for.
In my day jobs I frequently deal with bare metal systems in datacenters, so I want to replicate that in my homelab for better or for worse. This includes IPMI BMC/OOB connectivity, PXE booting, BIOS/UEFI stuff, hard drives and SSDs, real network routers and switches, writing tooling for all that stuff, and whatnot.
I don't need raw compute power nor storage, I just need lots of diverse systems. And since it's likely to be idle a lot of the time, it should be low power too.
A while back in 2012 I did take a HELMER drawer leftover from this project,
filled it full of 8x Raspberry Pis (1st gen), and created tinycluster.
(https://binaryfury.wann.net/tinycluster/)
Plus the form factor of the HELMER makes it fun to come up with ideas to fit things into a compact space.
The HELMER cabinet is about 11" wide, 27" tall, and 17" deep. It fits perfectly under an IKEA desk if you have one. Other than the power and Ethernet cables coming out the back, it's pretty self contained and stays within this footprint.
I'm not really sure. I wasn't keeping track of components and hardware when I originally built it, and I've replaced and expanded things over the years. I'm hoping by writing docs I can jog my memory and pin down material cost.
I think I estimated around $300 for the HELMER cabinet, all the extra metal, acyrlic, cabling, screws, hardware, and including the 16-port switch and router. Then whatever the individual system cost, in terms of motherboard + RAM + drives.
Aside from the electronics, I think the several feet of aluminum angle stock was the most expensive part.
I did the entire initial cabinet modification and a couple of working blades in a Sunday afternoon + evening. The power wiring is what takes the longest time, but you only have to do it once.
Last time I checked when it had 9 motherboards was around 260-280 watts continuously. It varies based upon how many hard drives vs SSDs are installed, and types of motherboards. In summer it can heat up the room so sometimes I'll turn off blades I'm not actively using.
An individual Avoton C2558 blade + SSD draws about 12.5 watts, and an older Atom 2550 + 3.5" HDD + 2.5" SSD draws about 28 watts.
Pretty quiet, I never notice it. The hard drives seeking around are about the only noise that come from it. Ironically the original goal for this was to get as quiet as possible because this is in my bedroom, now I have a circulation fan and HEPA air filter running all the time which are considerably louder.
The main thing is using mini-ITX form factor, as they're the only thing that fits with room for the drives. There's an assortment, altho usually almost all are embedded Intel Atom motherboards, either older D2500s or a couple of newer Avoton D2550s from Supermicro. There's a couple of old Pentium E6500s in there too that I bought from surplus.
Some motherboards have built-in 12 VDC inputs which could save using a PicoPSU. I considered them, but then I wouldn't be able to power dual hard drives.