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Andrew File System CSS534 Zach Ma
History • Originated inOctober 1982, by the Information Technology Center (ITC) formed withCarnegie Mellon and IBM Corporation • Commercialized by Transarc Corporation in 1989 and then made into an IBM product that was extensively used in the 1990s. • Made open-source by IBM under the name OpenAFS in 2000, and continues to be in widespread use at Carnegie Mellon and many other institutions.
General Goals • High availability • Ease of expansion • Incorporation of new technologies • Good performance even during peak periods • With graceful response to overload
Design Choices • Make the file system compatible with UNIX at the system call level • Use whole files as the basic unit of data movement and storage, rather than some smaller unit such as physical or logical records • Implement it with many relatively small servers rather than a single large machine
Servers and Clients • Two basic classes of machines • File server machines • Client machines • File server machines provide file storage and delivery service, along with other specialized services, to the other subset of machines in the network, the client machines • There are generally many more client workstations than file server machines.
Server Processes • File Server • Basic OverSeer Server(BOS Server) • Protection Server • Volume Server • Volume Location Server(VL Server) • Salvager • Update Server • Backup Server
File Server • Delivering and storing files • Maintaining the hierarchical directory structure • Handling all types of file requests • Keeping track of status information • Validating user identity • Creating symbolic and hard links between files
Basic OverSeer Server(BOS Server) • Constant monitoring on the other server processes • Automatic incident response • Interacting with system administrator • Helps system administrators to manage system configuration information
Client Processes – Cache Manager • Only component that resides on client machines • Main duty is to translate file requests (made by application programs on client machines) into remote procedure calls (RPCs) to the File Server. • Cache files before passing data on to the application program • Track the state of files
Cells and Volumes • Cell • A cell is an administratively independent site running AFS. • Volume • A unit of disk space that functions like a container for a set of related files, keeping them all together on one partition. • Can vary in size, but smaller than a partition.
Other Parts Required • Kerberos KDC (Key Distribution Center) • Performs two main functions related to network security • Verifying the identity of users • Providing methods to achieve mutual authentication • Network Time Protocol Daemon(NTPD) • Guarantee that all of the file server machines and client machines agree on the time
Updating Copies of Cached Files ->Y ->Z X X ->Y ->Z
Summary • Pros: • Scalability • Security • Reliability • Availability • Cons: • Authentication may cause problems • Conflicts with UNIX file semantics
References •  Howard, John H. An overview of the andrew file system. Carnegie Mellon University, Information Technology Center, 1988. •  Administrator Guide, http://docs.openafs.org/index.html •  User Guide, http://docs.openafs.org/index.html •  http://en.wikipedia.org/wiki/Andrew_File_System •  http://www.cmu.edu/corporate/news/2007/features/andrew/history_overview.shtml