As high-performance computing increases in popularity and performance, the demand for similarly capable input and output systems rises. Parallel I/O takes advantage of many data server machines to provide linearly scaling performance to parallel applications that access storage over the system area network. The demands placed on the network by a parallel storage system are considerably different than those imposed by message-passing algorithms or datacenter operations; and, there are many popular and varied networks in use in modern parallel machines. These considerations lead us to develop a network abstraction layer for parallel I/O which is efficient and thread-safe, provides operations specifically required for I/O processing, and supports multiple networks. The Buffered Message Interface (BMI) has low processor overhead, minimal impact on latency, and can improve throughput for parallel file system workloads by as much as 40% compared to other more generic network abstractions.