Degraded-First Scheduling for MapReduce in Erasure-Coded Storage Clusters

We have witnessed an increasing adoption of erasure coding in modern clustered storage systems to reduce the storage overhead of traditional 3-way replication. However, it remains an open issue of how to customize the data analytics paradigm for erasure-coded storage, especially when the storage system operates in failure mode. We propose degraded-first scheduling, a new MapReduce scheduling scheme that improves MapReduce performance in erasure-coded clustered storage systems in failure mode. Its main idea is to launch degraded tasks earlier so as to leverage the unused network resources. We conduct mathematical analysis and discrete event simulation to show the performance gain of degraded-first scheduling over Hadoop's default locality-first scheduling. We further implement degraded-first scheduling on Hadoop and conduct test bed experiments in a 13-node cluster. We show that degraded-first scheduling reduces the MapReduce runtime of locality-first scheduling.