If you need to store many TeraBytes of data yearly the cheapest and most reliable option is getting an LTO tape drive. The drive itself is expensive if you buy it new like a LTO-6 (2.5TB) or LTO-7 (6TB). The tapes are cheap and read/writing is very fast (seeking being a tape is not as fast as an hard disk of course but it rarely takes more than 60-80seconds on average). There are used LTO-3 (400GB) , LTO-4 (800GB) tape drives at cheap prices on eBay while the LTO-5 (1.5TB) ones are more expensive. LTO-5, LTO-6, LTO-7 feature LTFS file system to virtualize access to the tape drive like it was a removable disk unit.