【作者】 秦磊华；

【导师】 余胜生；

【作者基本信息】 华中科技大学 ， 计算机系统结构， 2007， 博士

【摘要】 SAN具有高性能、易扩展、高可靠等优点,已成为主流网络存储技术之一,广泛应用于各类数据中心,以满足企业日益增长的信息对大容量、高性能存储系统的需求。然而,数据丢失的风险随着存储容量的增加而增加,为了降低数据丢失风险、提高数据和应用系统的可用性,人门正在研究基于高速广域网的SAN互连,以构建基于存储广域网的远程数据镜像、备份和文件共享。目前,常用的三种存储扩展技术是基于IP、基于同步光纤网和基于波分复用的存储扩展,从协议层次上看,前者采用IP协议承载FC协议、后者直接将FC协议通过光载波传输、而新一代的同步光纤网使用透明通用成帧规程GFP T (Transparent General Framing Procedure)将FC协议映射到SONET中传输。与一般网络应用相比,存储扩展的特殊性主要有两点,其一是数据传输量大,需要网络具有高吞吐率;其二是可靠性要求高。流量控制是实现存储扩展应用中平滑数据流量、提高网络吞吐力和数据传输可靠性的重要技术手段。研究表明,存储扩展应用中的IP网络具有高带宽时延积特性,该环境下,传统TCP协议受其窗口字段数据位长度的限制不能充分利用网络带宽,必须采用高速TCP协议。运用理论分析和仿真相结合的方法,研究了高速TCP协议对高带宽时延积网络的适应性,包括路由器缓存的需求、协议的公平性以及光突发交换网络对TCP协议的影响等内容。研究结果表明:(1)路由器的缓存容量只要不低于网络带宽时延积的10%,扩展链路带宽的利用率就能达到90%以上;(2)常见的四种高速TCP协议中,公平性由高到低的次序是FAST TCP、HSTCP、BIC TCP、STCP。采用自动队列管理能有效降低同步丢包的概率,提高TCP协议的公平性;(3)虽然光突发交换网的偏置时间和封装时间会对存储扩展性能产生一定的影响,但光网络的高稳定性和低丢包率有利于性能的提高,因此,采用光网络对IP存储扩展性能影响不大。上述研究结果表明,基于高速TCP协议的IP存储扩展可以在现有IP网络构架下实施,研究结果也为选择具体的TCP协议,实施基于IP的存储扩展提供了依据。不同于IP网络,基于波分复用和基于SONET的存储扩展采用的是基于信用(Credit)的流量控制协议。研究表明,传统FC流量控制协议采用固定分配Credit的方法,导致存储扩展性能低、连路利用率不高。针对上述不足,提出了一种C23+模式的改进算法,新算法根据扩展链路的距离和带宽分配Credit,并将FC协议中的相对Credit更新策略修改成绝对更新策略,对的更新周期也进行了调整,理论分析表明,修改后的流量控制协议不仅能消除Credit更新信息丢失的累积效应,而且还能有效控制缓冲区上溢、缓冲区下溢、Credit下溢。Credit在采用GFP T的SONET存储扩展应用中,GFP T网关和附接的FC设备之间采用的是基于Credit的流量控制协议,而两个GFP T网关之间使用的是简单流量控制协议ASFC(Alternate Simple Flow Control),分析发现,ASFC流量控制协议存在下列不足:(1)不能控制目标GFP T网关缓冲区的溢出;(2)流量控制原语的触发条件没有与目标GFP T网关设备的拥塞相关联。针对上述不足,提出了一种优化方法,使GFP T网关缓存容量的分配与链路距离及带宽相关联,同时还使ASFC流控原语的触发条件与FC设备的数据拥塞和目标GFP T网关数据拥塞关联。在上述研究的基础上,构建了基于粗波分复用的存储扩展原型系统,并对远程访问性能进行了测试。更多还原

【Abstract】 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.更多还原