File Transfer

A common problem for many scientific applications is the replication of - often large - data sets (files) from one system to another. (For the generalized problem of transferring data sets from a source to multiple destinations, see DataDissemination.) Typically this requires reliable transfer (protection against transmission errors) such as provided by TCP, typically access control based on some sort of authentication, and sometimes confidentiality against eavesdroppers, which can be provided by encryption. There are many protocols that can be used for file transfer, some of which are outlined here.

  • FTP, the File Transfer Protocol, was one of the earliest protocols used on the ARPAnet and the Internet, and predates both TCP and IP. It supports simple file operations over a variety of operating systems and file abstractions, and has both a text and a binary mode. FTP uses separate TCP connections for control and data transfer.
  • HTTP, the Hypertext Transfer Protocol, is the basic protocol used by the World Wide Web. It is quite efficient for transferring files, but is typically used to transfer from a server to a client only.
  • RCP, the Berkeley Remote Copy Protocol, is a convenient protocol for transferring files between Unix systems, but lacks real security beyond address-based authentication and clear-text passwords. Therefore it has mostly fallen out of use.
  • SCP is a file-transfer application of the SSH protocol. It provides various modern methods of authentication and encryption, but its current implementations have some performance limitations over "long fat networks" that are addressed under the SSH topic.
  • BitTorrent is an example of a peer-to-peer file-sharing protocol. It employs local control mechanisms to optimize the global problem of replicating a large file to many recipients, by allowing peers to share partial copies as they receive them.
  • VFER is a tool for high-performance data transfer developed at Internet2. It is layered on UDP and implements its own delay-based rate control algorithm in user-space, which is designed to be "TCP friendly". Its security is based on SSH.
  • UDT is another UDP-based bulk transfer protocol, optimized for high-capacity (1 Gb/s and above) wide-area network paths. It has been used in the winning entry at the Supercomputing'06 Bandwidth Challenge.

Several high-performance file transfer protocols are used in the Grid community. The "comparative evaluation..." paper in the references compares FOBS, RBUDP, UDT, and bbFTP. Other protocols include GridFTP, Tsunami and FDT. The eVLBI community uses file transfer tools from the Mark5 software suite: File2Net and Net2File. The ESnet "Fasterdata" knowledge base has a very nice section on Data Transfer Tools, providing both general background information and information about several specific tools. Another useful document is Harry Mangalam's How to transfer large amounts of data via network—a nicely written general introduction to the problem of moving data with many usage examples of specialized tools, including performance numbers and tuning hints.

Network File Systems

Another possibility of exchanging files over the network involves networked file systems, which make remote files transparently accessible in a local system's normal file namespace. Examples for such file systems are:

  • NFS, the Network File System, was initially developed by Sun and is widely utilized on Unix-like systems. Very recently, NFS 4.1 added support for pNFS (parallel NFS), where data access can be striped over multiple data servers.
  • AFS, the Andrew File System from CMU, evolved into DFS (Distributed File System)
  • SMB (Server Message Block) or CIFS (Common Internet File System) is the standard protocol for connecting to "network shares" (remote file systems) in the Windows world.
  • GPFS (General Parallel File System) is a high-performance scalable network file system by IBM.
  • Lustre is an open-source file systems for high-performance clusters, distributed by Sun.

References

-- TobyRodwell - 2005-02-28
-- SimonLeinen - 2005-06-26 - 2015-04-22

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