Abstract

The Alex filesystem provides users and applications transparent read access to files in Internet anonymous FTP sites. Today there are thousands of anonymous FTP sites with a total of a few million files and roughly a terabyte of data. The standard approach to accessing these files involves logging in to the remote machine. This means that an application can not access remote files and that users do not have any of their aliases or local tools available when connected to a remote site. Users who want to use an application on a remote file must first manually make a local copy of the file. Not only is this inconvenient, it creates two more problems. First, there is no mechanism for automatically updating this local copy when the remote file changes. The users must keep track of where they get their files from and check to see if there are updates, and then fetch these. Second, many different users at the same site may have made copies of the same remote file, thus wasting disk space. Alex addresses the problems with the above approach while maintaining compatibility with the existing FTP protocol so that the large collection of currently available files can be accessed. To get reasonable performance, long term file caching must be used. Thus consistency must be addressed. Traditional solutions to the cache consistency problem do not work in the Internet FTP domain: callbacks are not an

Citations

760	Scale and performance in a distributed file system - Howard, Kazar, et al. - 1988
190	World-Wide Web: The Information Universe - Berners-Lee, Cailliau, et al. - 1992
28	NFS: Network File System Protocol specification - Nowicki - 1989
19	A measurement study of Internet file transfer traffic - Ewing, Hall, et al. - 1992
14	The Siphon: Managing distant replicated repositories. Research report 7, Paris Research Laboratory, Digital Equipment Corp - Prusker, Wobber - 1991
4	The Jade File System - Rao - 1989
3	alex/edu/indiana/bio/fly/util/mac/hyperftp.readme, see also /alex/edu/ sdsu/ucselx/pub/mac/HyperFTP.sit.Hqx - Hornig, “HyperFTP” - 1990
3	Hyperbole Manual - Hypertext for Everyday Work - Weiner - 1991
1	Revised - Alberti, Anklesaria, et al. - 1991
1	Wide Area Information Servers”, Thinking Machines - Kahle - 1991