This paper explores interposed request routing in Slice, a new storage system architecture for high-speed networks incorporating network-attached block storage. Slice interposes a request switching filter | called a /iproxy | 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 /xproxy to virtualize the standard Network File System (NFS) protocol, presenting to NFS clients a unified shared file volume with scalable bandwidth and capacity. Experimental results from the industry-standard 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.