dfig.doc - DRAFT 2 Distributed filing in the Grid Grid...

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DRAFT 2 Distributed filing in the Grid Grid computing is characterized by ultrafast computers connected via ultrafast networks. Distributed computations now being planned, such as the ATLAS LHC experiments, anticipate producing several terabytes each day and distributing this in petabyte-scale Atlas data stores around the world. Based on software and human processes, Grid data management technologies can not keep pace with hardware-driven advances in processing, network, and storage. Today's state of the art in Grid data management is parallel FTP driven manually or by scripts. FTP has the advantage of a long history, a strict and simple standard, and vendor support across the board. However, FTP has some fundamental inadequacies, such as its protection model, which uses a login/password pair to initiate a session, and seems to require global agreement on a name space for all Grid users. In this note, we review the terminology and goals of distributed file systems and identify viable alternatives for distributed filing in the Grid. Overview of file systems The ability to store data permanently has always been fundamental to information technology. The file system is the part of an operating system that offers permanent storage. To allow files to be shared and reused, the file system arranges stored objects in such a way that they can be named. The file system is obliged to guarantee that a file and its name will exist from the time that it is created until the time that it is destroyed. A local file system is one that resides entirely on one computer and is accessed from that computer. Local file systems using magnetic disk is fast, inexpensive, and reliable. Technology advances have made hundreds, even thousands of megabytes available on credit card sized devices, so that one's personal files can be carried in a purse or a shirt pocket. Notwithstanding these advantages of local file systems, there are many disadvantages of entrusting storage to local file systems. A major concern is the security and integrity of data. A file system carried in a shirt pocket risks loss or corruption. Important data must be backed up onto archival media at regular intervals to insure against loss, but the sad fact is that most individuals do not care to be saddled with system administration. Another problem with local file systems is the clumsiness associated with sharing. When many users share a single computer, file sharing can be easy and natural, but in an environment such as the Grid, which is rich with distributed computers, sharing files entails exchanging disks or tapes, or explicitly transferring copies of files among users on a network. The proliferation of copies can make it quite a challenge to determine the current copy.
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  • Spring '14
  • file systems

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