Calculating total permanent storage

[cpereyra5199]

I have been watching videos and getting information on the temp storage SSDs and figuring out how many plots each can handle. However, I don't see much information about how much total permanent storage I should have. Can someone point me to somewhere where I can find this information or provide some detail on how I would go about calculating how much total permanent storage I would need? Also, as far as permanent storage goes, I'v read something about switching drives out, shouldn't drives stay plugged in in order to use the plot that was already put on the drive? I have bought 4 5TB external drives and I am wondering if I can combine those into one volume or would I need to swag them out as they get filled up and then leave them all plugged in when it is finished? Sorry for the newbie questions but I have not found much information about this part of the plotting process.

Thank you,.