October update
I filled up the TR-004 I mentioned previously after having to wipe the file system. I have also got the last one refilling, weather permitting. I've installed Raspberry Pi OS based upon Debian Trixie on all the Rpi harvesters now. I managed to preserve the btrfs file system and reinstalled everything from scratch on them. Current setup: 2 x Raspberry Pi4 (4GB), two external USB 16TB HDD each running btrfs in single mode. 4 x Raspberry Pi5 (8GB), TR-004 with 4 x 16TB HDD each running btrfs in raid0. 1 x Ryzen 3600 with 10 x 20TB HDD running zfs in raidz2. 1 x Intel i3 with 7 x 8TB HDD running zfs in raidz1. Tomorrow is forecast to be 33 degrees C so I'll be powering the farm down for a bit.