The document discusses erasure coding as an alternative to replication in distributed storage systems like HDFS. It notes that while replication provides high durability, it has high storage overhead, and erasure coding can provide similar durability with half the storage overhead but slower recovery. The document outlines how major companies like Facebook, Windows Azure Storage, and Google use erasure coding. It then provides details on HDFS-EC, including its architecture, use of hardware acceleration, and performance evaluation showing its benefits over replication.