Study on the data flow balance in NFS server with iSCSI
ICA3PP'12 Proceedings of the 12th international conference on Algorithms and Architectures for Parallel Processing - Volume Part I
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A pass-through server such as an NFS server backed by an iSCSI[1] storage server only passes data between the storage server and NFS clients. Ideally it should require at most one data copying operation on sending or receiving, as in normal IP routers. In practice, pass-through servers actually incur multiple data copying operations because they are implemented using a layered architecture where each layer has its own internal data representation. This paper describes the design, implementation and evaluation of a novel network-centric buffer caching scheme called NCache that minimizes data copying overhead in pass-through servers without requiring significant changes to their existing implementation. By organizing the data being passed or cached in a network friendly format, NCache is able to eliminate all unnecessary data copying. The key innovation in NCache is that it exploits the fact that pass-through servers do not interpret data, by replacing physical copying with logical copying in a way transparent to existing software. This transparency enables NCache to be easily portable to many operating systems. We have successfully built a Linux-based NCache prototype that can be applied to in-kernel NFS and static Web servers. Empirical performance measurements collected from this prototype show that by reducing the CPU load associated with data copying, NCache is able to provide up to 92% improvement in throughput for NFS server and up to 47% for Web server.