R. Y. Wang, T. E. Anderson.
xFS: A Wide Area Mass Storage File System.
Proc. Fourth Workshop on Workstation Operating Systems
pp. 71-78.
October 1993.
Also appeared as University of California Technical Report CSD-93-783.
The current generation of file systems are inadequate in facing the
new technological challenges of wide area networks and massive
storage. WANs have lower bandwidth, higher latency, and higher
cost. Such a scarce resource must be used intelligently. The
management of a large number of hosts and massive amount of data
demands a system with good scalability. And as the system is made more
scalable, allowing larger groups of clients and servers to work
together, it also becomes more likely at any given time that some
hosts will be unable to communicate. Existing disk-based local area
network file systems fail to distinguish the difference between WAN
communication and LAN traffic and generate excessive traffic over the
WAN links. They depend on central server models that offer poor
scalability and availability. Although some systems do offer limited
tertiary support, such features are usually based on ad hoc extensions
to disk-based data structures and the result is usually less than
satisfactory. We are currently implementing xFS, a prototype wide area
mass storage file system. Our goal in xFS is to provide the
performance and availability of a local disk file system when sharing
is minimum and storage requirement is small. It adapts many of the
techniques used in the field of high performance multiprocessor
design. xFS organizes hosts into a hierarchical structure so locality
within clusters of workstations can be better exploited. By using an
invalidation-based write back cache coherence protocol, xFS minimizes
network usage. It exploits the file system naming structure to reduce
cache coherence state. xFS integrates different storage technologies
in a uniform manner. Data is located by using a translation mechanism
similar to that of virtual-to-physical mapping of memory
management. Storage is managed in a log-structured manner for fast
write performance. Due to its intelligent use of local hosts and local
storage, we expect xFS to achieve better performance and availability
than current generation network file systems run in the wide area.