Perfomance analysis and optimization of flow control in SAN extension based on WDM

Abstract

Fibre Channel (FC)becomes the main storage protocol of SAN(Storage Area Network).Enterprises are increasingly deploying FC-SANs in their data central. In order to mitigate the risk of losing data, more and more enterprises are increasingly adopting storage extension technologies based on WDM (Wavelength Division Multiplexing) to replicate their business critical data to a secondary site. Storage Extension based on WDM makes use of the flow control mechanism based on Credit, it offers immediate access to the full link bandwidth without a ramp-up time ,but the updating frequency of Credits and the throughput of storage extension are limited by the long extension distances. Adding the receiver memory can remove those limitations, but it also brings about the long queuing time. In this paper, a Petri-Net model of FC flow control protocol is constructed to analysis the relative degree between the storage extension performance with bandwidth, distance and initial number of Credit. Meanwhile, a new integrative flow control mechanism for storage extension based on WDM is proposed, it is consists of three flow control loop A,B and C. A is deployed between FC sender and WDM ingress gateway, B takes affection on the WDM ingress gateway and WDM engress gateway, C works among WDM engress gateway and FC receiver, and the three flow control loop are integrated by the buffer utilization of ingress and engress gateway. Theoretical analysis and simulation result show that the new flow control method can effectively remove distance limitation and allow data traffic to flow at maximum throughput without adding queuing latency. The new flow control method is implemented in WDM gateway, it is transparent for FC protocol and can provide a good compatibility.