BSDCon 2002 Abstract
Design And Implementation of a Direct Access File
System (DAFS) Kernel Server for FreeBSD
Kostas Magoutis, Division of Engineering and Applied Sciences, Harvard
The Direct Access File System (DAFS) is an emerging commercial standard
for network-attached storage on server cluster interconnects. The DAFS
architecture and protocol leverage network interface controller (NIC) support
for user-level networking, remote direct memory access, efficient event
notification, and reliable communication. This paper describes the design
of the first implementation of a DAFS kernel server for FreeBSD, using
existing interfaces with minor kernel modifications. We experimentally
demonstrate that the current server structure can attain read throughput
of more than 100 MB/s over a 1.25 Gb/s network even for small (i.e. 4K)
block sizes when prefetching using an asynchronous client API. To reduce
multithreading overhead and integrate the NIC with the host virtual memory
system, our forthcoming system will incorporate new FreeBSD kernel support
for asynchronous vnode I/O interfaces, integrating network and disk
event notification and handling, and VM support for remote direct memory
access. We believe our proposed kernel support is necessary to scale event-driven
file servers to multi-gigabit network speeds.
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