© 2000 E-flow ACM (Association for Computing Machinery).All right reserved. This paper explores interposed request routing in Slice, a new storage system architecture for high-speed networks incorporating networkattached block storage. Slice interposes a request switching filter — called a ßproxy — along each client's network path to the storage service (e.g., in a network adapter or switch). The ¿¿proxy intercepts request traffic and distributes it across a server ensemble. We propose request routing schemes for I / O and file service traffic, and explore their effect on service structure. The Slice prototype uses a packet filter pproxy to virtualize the standard Network File System (NFS) protocol, presenting to NFS clients a unified shared file volume w i t h scalable bandwidth and capacity. Experimental results from the industrystandard SPECsfs97 workload demonstrate that the architecture enables construction of powerful network-attached storage services by aggregating cost-effective components on a switched Gigabit Ethernet LAN.