Direct Access File System (DAFS): Duke University Demo

• Source-release reference implementation of DAFS• Broader research goal: Enabling efficient and transparently

scalable Internet-based storage and content services• Example applications built on TPIE framework

– Merge– TerraFlow – GIS

• DAFS vs. NFS

Participants: Jeff Chase, Richard Kisley, Andrew Gallatin,Rajiv Wickremesinghe, Darrell Anderson, Ken Yocum.Collaborators: Margo Seltzer, Norm Hutchinson.Funding provided by Network Appliance and bythe National Science Foundation under grant EIA-9870724 (ESS),with infrastructure support from EIA-9972879 (RI).

DAFS Demo Testbed

DAFS / NFSClient

256MB SDRAM

DAFS / NFSServer

512MB SDRAM

cLAN

GigEther

86 MB/s

Testbed allows direct comparison of DAFSand NFS applications

User Space

OS Kernel

PCI Bus

NIC

TPIE: One Application–Two File Systems

DMA

User Applications

TPIE Library

cLAN VIA Adapter

DAFS Client

cLAN VIA

cLAN VIPL Library

cLAN Device Driver

DAFS Client Library

copyin/out

DMA

User Applications

TPIE Library

VFS/VM Buffercache

NFS

TCP/IP Stack

Ethernet Device Driver

Alteon Gigabit Ethernet Adapter

NFS Client

Ethernet

Benefits of DAFS• Low I/O overhead

– Copy-avoidance with RDMA

– Improves application performance up to 2x depending on the I/O demands of the application

– Benefits may be much higher since the NFS in our experiments is highly optimized

• User-level networking– Enabled by the Emulex/Giganet clan VI network

– Reduced protocol overhead on the host

– Reduced context switching on the host

TPIE Merge Application

• Key component of external sort algorithm– Basic primitive of many external memory applications

• Sequential I/O: reads and writes• Merge parameters control compute-I/O ratio

– Merge order increases complexity of merge computation

– Record density (records / MB) increases the number of merge computations that must be done between I/O’s