I just spun up my second node, and both nodes are running on separate RPi 4s ( both are 4GB RAM version). They are low power solutions, which is super nice. Both nodes have a single HDD connected via USB 3.0.
From everything I’ve gathered here on the forum is that for almost all situations using a raspberry pi, the recommendation is to use a single drive per node. Although using your two drives to total ~6TB sounds like a good idea (more storage space, right?), the risk for one drive failing leading to total data loss is too great.
Here are a few of the threads that this has been discussed on:
Therefore, I believe what the Storj group would recommend, is use the existing hardware you currently have (RPi 4 (2GB) with one of your HDDs) to start your first node. Let that get going for a while, and then if/when your node becomes full with data you could then choose to start a second node, although this might require another computer/Rpi. I know there has been some discussion on running two nodes on the same Rpi, but I think the biggest bottle neck would be the Rpi itself, ranging from low power CPU, your version only having 2GB of RAM, and then also the USB controller trying to handle the I/O of the two HDD traffic. The reasoning behind the “staggered” timing is that two nodes behind the same public IP are “seen” as a single location and satellites would end up splitting traffic to both nodes, i.e. taking twice as long to finish the vetting process and loading the nodes up with data.
Here’s a couple threads explaining that second node process:
Hope this helps, and hope you choose to join the Storj network! I’ve had a good time setting up my node and learning about the project over the past 8 months. Plan to be here for the long haul.