Structure and performance of the direct access file system
Kostas Magoutis, Salimah Addetia, Alexandra Fedorova, Margo I. Seltzer, Jeffrey S. Chase, Andrew J. Gallatin, Richard Kisley, Rajiv G. Wickremesinghe, Eran Gabber
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 function-
ality 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.