End of 2023 update
Farming continues. All disks are full. Currently I have 200TiB of disk space occupied. I have ordered a pair of QNAP TR-004 "NAS expanders". These are 4 bay expansion boxes that connect via USB. They can do RAID or be a JBOD, controlled via dip switches on the back. My idea is to try the Raspberry Pi's running them but I might just plug them into the secondary storage server. I may have wasted my money on these, but I will have to see how they work out. The 5 bay ORICO expansion box I have tends to overheat despite having a fan in the back. I have stopped using it now. The drive bay doors have most of the holes covered and the PCB at the back where the drives plug into the SATA connectors is solid so it blocks all air flow that the fan produces. It also has an annoying habit of putting the drives to sleep after 12 minutes. Lastly they were rather slow but that is probably because the USB connection is 5 Gbit and has to be shared between 5 drives. QNAP have a TL-D400S (4 b