Ben explaining the MapReduce pairs and stripes:
The concept of stripes is to aggregate data prior to the Reducers by using a Combiner. There are several benefits to this, discussed below. When a Mapper completes, its intermediate data sits idle when pairing until all Mappers are complete. With striping, the intermediate data is passed to the Combiner, which can start processing through the data like a Reducer. So, instead of Mappers sitting idle, they can execute the Combiner, until the slowest Mapper finishes.
Original title and link: MapReduce Pairs and Stripes Explained ( ©myNoSQL)