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USENIX 2002 Annual Conference - Technical Program Abstract
Structure and Performance of the Direct Access File System
Kostas Magoutis, Salimah Addetia, Alexandra Fedorova, Margo I. Seltzer,
Division of Engineering and Applied Sciences, Harvard University;
Jeffrey S. Chase, Andrew J. Gallatin, Richard Kisley, Rajiv G. Wickremesinghe,
Department of Computer Science, Duke University;
Eran Gabber,
Lucent Technologies - Bell Laboratories
Abstract
The Direct Access File System (DAFS) is an emerging industrial standard for network-attached storage. DAFS takes advantage of new user-level network interface standards. This enables a user-level
file system structure in which client-side functionality for remote data access resides in a library
rather than in the kernel. This structure addresses
longstanding performance problems stemming from
weak integration of buffering layers in the network
transport, kernel-based file systems and applications. The benefits of this architecture include
lightweight, portable and asynchronous access to
network storage and improved application control
over data movement, caching and prefetching.
This paper explores the fundamental performance characteristics of a user-level file system
structure based on DAFS. It presents experimental
results from an open-source DAFS prototype and
compares its performance to a kernel-based NFS
implementation optimized for zero-copy data transfer. The results show that both systems can deliver
file access throughput in excess of 100 MB/s, saturating network links with similar raw bandwidth.
Lower client overhead in the DAFS configuration
can improve application performance by up to 40%
over optimized NFS when application processing
and I/O demands are well-balanced.
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