I did a little Googling and, aside from Gemini telling me it isn't great, I can't find any information about the proposed configuration: I currently have a single NVME cache drive (1TB) and want to add a second. I will want to put them in a pool and partition the drives so that I have 8GB for boot and the rest can be my cache (after moving to 7.3.1). Is there something wrong with this idea?