Research On The Buffer Allocation Strategy Of Flow Control In Storage Extension

SAN(Storage Area Network) is the main network storage technology and has been widely used in the data center to meet the incremental requirements of the enterprise storage system with the large capacity, high performance. However, the risk of losing data will increase with the augumentation of storage capacity. In order to migrate the risk of losing data and improve the availability of data and application system, the connection of SAN based on high speed WAN for the aims of remote mirror, backup and file sharing has been researched.At present, the main techniques for storage extension are based on IP, SONET and CWDM respectively. From the perspective of the protocol level, the first method carry the FC(Fibre channel) protocol with the IP protocol, the new generation SONET maps the FC protocol into the SONET by transparent GFP(Generic Framing Procedure), and meanwhile the CWDM technique carry the FC protocol by optical network directly.Comparison with the conventional network application, the two special aspects the storage extension application are mainly expressed as follow: for one thing, it is necessary for the network to hold high throughput for the large amount of the data transmission. For another, the reliability is indispensable. Flow control is the important technique to smooth the data flow in network, enhance the network throughput and improve the reliability of the data transmission in the application of the storage extension. Research indicates that the IP networks for the storage extension have the character of high band latency production. Under such application background, the traditional TCP protocol can not make fully use of the network bandwidth for the constraint of data bit length of the window field, the high speed TCP protocol must be taken into consideration. For the high speed TCP protocol, the requirement of the router buffer, the fairness of the protocol and the influence of the optical switch network on the TCP protocol are studied by the methods of theoretical analyses and simulation. The study shows us that: (1) If the router buffer memory capacity is not lower than the 10% that of the band latency production, the utilization of the link bandwidth will achieve over 90%. (2) The sortorder of high speed TCP protocol fairness from high to low is FAST TCP, HSTCP, BIC TCP and standard TCP. The fairness of the TCP protocol can be improved through reducing the packet loss by using automatic queue management. (3)Although the offset time and assembly time of OBS(Optical Burst Switch) would have some effects on the storage extension performance, high stability and low packet loss of the OBS will help to improve the performance, therefore, the application of the optical network will have little influence on the storage extension performance. The above studies indicate that the IP storage extension with high speed TCP protocol can be deployed in current IP network infrastructure, and it also provide the guide for storage extension based on IP network.Different from IP network, the flow control protocol of the storage extension based on WDM and SONET are based on credit with static allocation strategy, which leads to the low performance and low utilization ratio of network. An new algorithm of credit allocation named C23+ has been put forward for storage extension based on SONET and WDM. In the new algorithm the Credit is allocated according to the distance and bandwidth of the extension link, the absolute update policy is replaced with the relative update policy in the FC protocol, the update cycle is also adjusted. Theoretical analyses result show us that the new flow control protocol can not only migrate the accumulation effects from the information lose of the Credit update, but also prevent the overflow of buffer and the underflow of buffer or Credit.In the SONET storage extension based on GFP T, the transfer control protocol between the GFP T gateway and the connected FC devices is based on Credit, meanwhile, the ASFC(Alternate Simple Flow Control) protocol is applied to between the GFT T gateways. Study indicates that there are two disadvantages for ASFC protocol:(1)The overflow of the target GFP T gateway buffer can not be prevented by ASFC flow control protocol. (2)The trigger condition of the flow control Primitive Signals are not related with the congest of the target GFT T gateway devices. A optimal method is presented, it allocates the credits for GFP T gateway according to distance and bandwidth of storage extension link, and it amendment the trigger condition of the flow control Primitive Signals of ASFC according to the congestion of FC devices and target GFT T gateway devices.Based on the above research, a storage extension prototype based on CWDM is implemented and the test is done for the evaluation the performance of the remote access.