Color me impressed … Seagate and their 60TB 3.5inch SAS drive. Yes, the 60 bay Unison units can handle this. That would be 3.6PB per 4U unit. 10x 4U per 48U rack. 36PB raw per rack. 100PB in 3 racks, 30 racks for an exabyte (EB).
The issue would be the storage bandwidth wall height. Doing the math, 60TB/(1GB/s) -> 6 x 104 seconds to empty/fill such a single unit. We can drive these about 50GB/s in a box, so a single box would be 3600TB/(50GB/s) or 7.2 x 104 seconds to empty/fill a box full. Network bandwidth would be the biggest issue … we could get 2x 100Gb NICs going full speed, but even that would still be 20% of where we need to be to keep it fully loaded.
This would need to be for an archive, and you’d need a mixture of object store and erasure codes on this. No way would you even consider a RAID on such a beast.