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iSCSI Performance in Integrated LAN/SAN Environment Li Yin U.C. Berkeley Outline Motivations Network Congestion and Disk Congestion differentiation iSCSI ns-2 Simulator Conclusion Future work Motivations Storage Area Network • • Hosts/Servers are connected to storage devices through network Advantages: • • • High availability Better resource sharing Easy to manage Transport SCSI over IP Networks • Less cost • Longer operating distance • Leverage existing technology and management tools Motivations (cont.) iSCSI is one of the most promising protocols to carry SCSI traffic over IP networks. SAN/LAN integration is one step towards SAN/WAN integration • • • Utilize existing Ethernet to carry iSCSI traffic Problem: • iSCSI performance degrades dramatically with cross traffic Challenge: • How to sustain high I/O throughput even with competing traffic? Why Performance Degrades? Resources are saturated • First step: where is the congestion point? • Cross traffic will compete for network bandwidth, disk, CPU and etc. Our hypothesis: Congestion caused by network and disk behave differently Second Step: how to avoid it? Test bed Setup Topology: Software Router Initiators Target Cisco iSCSI initiator Target machine runs IBM iSCSI target software driver A SCSI disk is attached to the target machine as the target disk Nistnet running on the software router to control delay, packet drop rate and etc. Experimental Setup iSCSI target disk is attached as raw device at the initiator • To filter out file system effect Rt Ri 16384 64KB random requests (1G data in total) • To reduce the cache effect Read Initiator: response time seen by the initiator Ri Tif Tir Tif: Initiator request finish time; Tir: Initiator request receive time Target: response time seen by the target iscsi driver Rt Ri Rt Ttf Ttr Ttf: Target request finish time; Ttr: Target request receive time Write Case 1: Network congestion Use packet drops to reflect network congestion Nistnet introduces uniform random packet drops The target disk performs no other disk operations Experimental Results initiator No drop 1% drop 5% drop target read write Case 2: Disk Competition Target machine continuously issue random I/O requests to the target disk No network interference is introduced Experimental Results initiator No drop, No compete 4KB Competing Request 4MB Competing Requests target read write Result Analysis initiator No drop, No Compete 4KB Competing Request 1% Drop target read write Congestion Caused by Network Target: How to improve performance when the degradation is caused by network? Our methodology: ns-2 based iSCSI simulator • Simulation can help us alleviate the limitation of available testbed configuration • Delay • Bandwidth Ns-2 iSCSI simulator iSCSI is implemented as a TCP application. • all iSCSI messages are encapsulated as an application message transmitted using TCP Start from a simple disk models • Parameters: • cache hit ratio • mean, variance, minimum processing time and maximum processing time for various request size Simulator Verification 16384 64KB random requests (1GB in total) Throughput Simulation Testbed Testbed Delay READ WRITE Impact of TCP Parameters Impact of minimum timeout value (minrto) • Real RTT is roughly 1.5ms Throughput 1s minrto # of Fast Retransmission 100ms minrto 10ms minrto # of Timeout 1ms minrto A more precise configuration of timeout value in LAN is useful, and is possible Conclusions iSCSI performance in LAN/SAN integrated environment is very important Performance degradation caused by network and disk is possible to be distinguished Ns-2 based simulator can match the real curve closely TCP parameter configuration have big impact on the performance Future Works Congestion point detection Simulation: • better monitoring point? • more complicated cross traffic • • • • More verification on write operations Bursty Drop Model More realistic system and disk model More analysis on how TCP will affect the performance? Future Work (Cont.) Design scheme to improve performance when congestion happens in network • Can we avoid packet drop? • • • • • Resource management? Shift to another target? • • Read: Multiple replica may exist Write: write to some target temporarily, re-organize data later QoS management Avoid iSCSI drop rate below some threshold If we have to, which packet to drop? • Leverage application layer information • • • Application importance iSCSI header packet vs. iSCSI data packet? Packets belong to same iSCSI data unit or multiple data units?