06-01-2014, 03:52 PM
Andrew File System
Andrew File .ppt (Size: 160 KB / Downloads: 15)
Introduction
Andrew File System (AFS) is one of the distributed file systems that been developed at Carnegie Mellon University (CMU) for use as a campus computing & the information system.
The design of AFS reflects an intention to support information sharing on a large scale by minimizing client-server communication.
It is designed to be heterogeneous, scalable, & it runs efficiently on variations on UNIX.
Main Goal:
AFS provide scalability to thousands of workstation at one site while offering users, applications & administrations the conveniences of a shared file system.
Whole-file caching
once a copy of a file or a chunk has been transferred to a client computer it is stored in a cache on the local disk. The cache contains several hundreds of the files most recently used on that computer. The cache is permanent, surviving reboots of the client computer. Local copies of files are used to satisfy clients’ open requests in preference to remote copies whenever possible.
Implementation
AFS is implemented as two software components that exist as UNIX processes called Vice and Venus.
Vice - name given to the server software that runs as a user-level UNIX process in each server computer
Venus - user-level process that runs in each client computer and corresponds to the client module.
Reliability
AFS supports a limited multiple residency for unchanging files. As servers go down, only non-replicated portions of the AFS filespace become inaccessible, leaving the rest of the file system intact. Replicated data is automatically fetched from one of the remaining servers. The clients automatically balance requests between all the servers containing a particular file.
Location database
Every server contains a copy of a fully replicated location database giving a mapping of volume name to servers. Temporary inaccuracies in this database may occur when a volume is moved, but they are harmless because forwarding information is left behind in the server from which the volume is moved.