This was a fun exercise, not sure if our WAG is in the right ball-park though, as some of the elements won’t have real price tags for a while. This was an intelligent guess based upon comparable systems pricing.
28x 4U 48 TB JackRabbit (JR4) units with 32 GB ram, 2x QDR IB ports, 2x SSD boot drives in a RAID1 + a “Velocibunny” MDS (1.5 TB of the fastest non-RAMdisk based server around) running Lustre. 1.344 PB raw capacity, 4 racks, 7 per rack.
Each box does 1.5 GB/s sustained to/from disk. Call it 1 GB/s out each IB port. 7 IB ports (ok 14 really) per rack, so 7 GB/s per rack, 4 racks, so 28 GB/s into the OSSes/OSTs.
Maybe pNFS will be ready by then …