A design structure embodied in a machine readable storage medium for designing, manufacturing, and/or testing a design for scheduling the servicing of data requests, using the variable latency mode, in an FBDIMM memory sub-system is provided. A scheduling algorithm pre-computes return time data for data connected to DRAM buffer chips and stores the return time data in a table. The return time data is expressed as data return time binary vectors with one bit equal to “1” in each vector. For each received data request, the memory controller retrieves the appropriate return time vector. Additionally, the scheduling algorithm utilizes an updated history vector to determine whether the received request presents a conflict to the executing requests. By computing and utilizing a score for each request, the scheduling algorithm re-orders and schedules the execution of selected requests to preserve as much data bus bandwidth as possible, while avoiding conflict.