Over the years I've used a handful of HP Micro servers to run a Linux-based web server application. To be honest I suspect it would comfortably run on a Pi, to give you some idea of power requirements. However it does need to be dependable and one of the criteria is RAID (software RAID 1 is fine).
We replace the hardware every few years so the question I have is: what is a good small server for Linux these days? Apart from the requirement to host 2 SATA drives there isn't much in terms of hardware requirements.
We don't even use a lot of disk space - maybe a few dozen GB. One HDD gets replaced annually so that no disk is older than 2y, using commodity disks in the 1-2TB range but partitioned to only use 200GB on each disk, just because we don't need more and it makes the swap to a new disk quicker. Hot swap not needed. Would consider SSD for the new server.
I was about to get a quote for an HP Gen10 MicroServer when it crossed my mind that maybe just buying the same server out of habit wasn't necessarily the right approach!