1) Accounting profit: revenue - expenses. This is colloquially what most people mean when they say "profit". To break even you just need to make enough money to cover your explicit expenses. In your example, you would need to make more in Filecoin income than you spent in disks/electricity/etc.
2) "Normal profit": this is a technical term in microeconomics. Basically this takes into account opportunity cost; the cost of not doing some other profitable thing with your time/money. By these standards, to break even you'd not only have to cover the cost of disks/electricity but also the "opportunity costs" of whatever else you could have been doing with those disks/electricity (like mining Bitcoin), or whatever you could have been doing if you never even purchased those disks to begin with (like investing in the S&P or whatever).
3) "Excess" or "economic" profits. These are extra profits on top of whatever you earn in #2. This is the part that goes to 0 for commodities like milk/gasoline/Filecoin but is non-zero for differentiated products like iphones.
For Filecoin specifically, I would expect that normal profits would probably be above the raw costs of disks and electricity, since it takes some effort to purchase and administer all that hardware, but probably below the cost of renting a VPS, since a VPS is typically used for more profitable things than just sitting around and holding stuff on disk.
