SPIRAL: A Client-Transparent Third-Party Transfer Scheme for Network Attached Disks

Third-party transfer is a data transfer mechanism where the party initiating the transfer is neither the source nor the sink for the data. In this paper, we present a scheme for supporting third-party transfers on storage systems with network-attached disks (NADs), called SPIRAL 1. SPIRAL allows NADs to send data directly to clients without going through the server. It is transparent to clients and relies only on the linear block interface of the current disks (or the future iSCSI disks). SPIRAL requires no porting of filesystem or application-level functionality to NADs and requires only simple modifications to server applications. To illustrate our approach, we implemented a prototype system on PCs running Linux. We present experimental results for NFS and HTTP on the prototype to demonstrate the effectiveness of our approach.