SSD for temporary storage
This build will be targeting 8 plots in parallel, and requires ~332GiB per process for a total temporary space requirement of 2665GiB or 2.85TB.
3x 960GB SATA
Preference of Intel S4510, S4610, or Samsung or Micron datacenter – target sub $100 each on eBay used
Amazon prime only - SK hynix Gold S31 1TB x 3 ($80 each). With 600TBW each, this should be adequate for 75-450TB of total plots combined
6x 480GB would also work, but would consume more SATA lanes than the chipset and would require an HBA like 9200-8i ($20)
2x 2TB M.2 NVMe
Preference for 1.92TB Samsung PM983 / 983 DCT. Make sure your motherboard supports 2x 110mm M.2 slots! Multiple M.2 can be put on a PCIe add-in-card as well, like this one from ASUS (it doesn’t work with all motherboards; check carefully before purchase).
Find any consumer NVMe that has >1000TBW per drive. Make sure you use the SSD endurance sheet to model how much you are going to be plotting. For small scale farms (100-200TB) this should be plenty of endurance.
1x 3.2 or 3.84TB U.2 NVMe - this is the preferred option, but slightly more expensive than the first two, and requires some used hardware hunting skills.
Preference is the Intel SSD D7-P5510 (brand new, harder to find but will get easier in 2021), Intel SSD DC P4610, Samsung PM1725b or any other mixed workload (3 DWPD endurance) class NVMe. This is going to be in the U.2 form factor and desktop motherboards will require an appropriate adapter: (this PCIe add-in-card to U.2 adapter works as well)
DiLinKer M.2 to U.2 I’ve used this on dozens of desktops and drives with no issues at PCIe 3.0 x4 (not tested yet at PCIe 4.0 x4)
PCIe x4 Card for U.2 (ex: StarTech PEX4SFF8639)
THIS IS THE HARDEST PART OF THE BUILD to get under $400. You will have to do some ninja shopping on eBay, but this is very doable. Anything that is 3.2TB or above that is on the endurance spreadsheet with high TBW will work
Thermals for temp drives. NVMe SSDs get hot with sustained write workloads. Monitor temps through smartmontools (sudo smartctl -a /dev/nvme0n1) or NVMe-CLI (sudo nvme smart-log /dev/nvme0n1). If your NVMe drive is getting above 70C and triggering the NVMe SMART critical temp warning, you need to add an additional fan to your desktop or directly on top of the U.2 NVMe.