  This paper explores the changes required of TCP to efficiently support
cluster file systems such as Hadoop Distributed File System (HDFS) where the
storage nodes are connected through a software defined networking (SDN).
Traditional chain replications in these file systems incur large delay and
cause inefficient network use. But SDN can cooperate with the cluster file
systems to address the problems by pre-arranging a distribution tree, which
opens the possibility of parallel replication. Unfortunately, it cannot be
realized without extending TCP, to accommodate the parallel transfer on the
transport layer. This paper discusses how to extend TCP to make it possible,
and demonstrates the feasibility by implementing a prototype in the Linux
kernel. The prototype saves the data replication time by 25% while
substantially reducing network use.
