Rack-aware MSR codes with optimal access

We derive a lower bound on the amount of information accessed to repair a single failed node from any number of helper racks in the rack-aware storage model that allows collective information processing in the nodes that share the same rack. Furthermore, we construct a family of rack-aware MSR codes with the number of symbols accessed for repair attaining the bound with equality for all admissible parameters. Constructions of rack-aware optimal-access MSR codes were only known for limited parameters.