GridFTP is a high-performance, reliable data transfer protocol optimized for high-bandwidth wide-area networks. Based on the Internet FTP protocol, it defines extensions for highperformance operation and security. The Globus implementation of GridFTP provides a modular
and extensible data transfer system architecture suitable for wide area and high-performance environments. GridFTP is the de facto standard in projects requiring secure, robust, high-speed bulk data transport. For example, the high energy physics community is basing its entire tiered data movement infrastructure for the Large Hadron Collider computing Grid on GridFTP; the Laser Interferometer Gravitational Wave Observatory routinely uses GridFTP to move 1 TB a day during production runs; and GridFTP is the recommended data transfer mechanism to maximize data transfer rates on the TeraGrid. Commonly used GridFTP clients include globus-url-copy, uberftp, and the Globus Reliable File Transfer service. In this paper, we present a Globus XIO based client to GridFTP that provides a posix-like
(open/close/read/write) interface to the users. Such a client greatly eases the addition of GridFTP support to third-party programs, such
as SRB and MPICH-G2. Further, this client provides an easier and familiar interface for applications to efficiently access remote files. We compare the performance of this client with that of globus-url-copy on multiple endpoints in the TeraGrid infrastructure. We perform both memory-to-memory and disk-to-disk transfers and show that the performance of this posix-like client is comparable to that of globus-url-copy. We also show that our GridFTP client significantly outperforms the GPFS WAN on the TeraGrid.