I obtained a used Dell PowerEdge and just stuffed a bunch of drives in there. It's old enough that the RAM is not overly expensive (DDR3), so it has 192GB of RAM to effectively cache the data, and then 32TB of raw storage. (Of course I regret not spending the extra money to take it to 384GB now.)

The nice thing about the array being big is that I can just RAID 1 it instead of worrying about tinkering with RAID 5, and leave a drive as a hot spare.

PCIe 2.5G NIC for the uplink, and then it can serve over SMB or iSCSI. The main use case for this thing, incidentally, is it just is a caching proxy that holds Docker images, models off of Huggingface, and so on.