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iSCSI Performance in Integrated LAN/SAN Environment

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

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iSCSI Performance in Integrated LAN/SAN Environment

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  1. iSCSI Performance in Integrated LAN/SAN Environment Li Yin U.C. Berkeley

  2. Outline • Motivations • Network Congestion and Disk Congestion differentiation • iSCSI ns-2 Simulator • Conclusion • Future work

  3. 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

  4. 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?

  5. Why Performance Degrades? • Resources are saturated • Cross traffic will compete for network bandwidth, disk, CPU and etc. • First step: where is the congestion point? • Our hypothesis: Congestion caused by network and disk behave differently • Second Step: how to avoid it?

  6. Software Router Initiators Target Test bed Setup • Topology: • 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.

  7. Rt Rt Ri Ri Experimental Setup • iSCSI target disk is attached as raw device at the initiator • To filter out file system effect • 16384 64KB random requests (1G data in total) • To reduce the cache effect • Initiator: response time seen by the initiator Tif: Initiator request finish time; Tir: Initiator request receive time • Target: response time seen by the target iscsi driver Ttf: Target request finish time; Ttr: Target request receive time Read Write

  8. 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

  9. Experimental Results initiator No drop 1% drop 5% drop target read write

  10. Case 2: Disk Competition • Target machine continuously issue random I/O requests to the target disk • No network interference is introduced

  11. Experimental Results initiator No drop, No compete 4KB Competing Request 4MB Competing Requests target read write

  12. Result Analysis read initiator No drop, No Compete 4KB Competing Request 1% Drop target write

  13. 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

  14. 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

  15. Simulator Verification • 16384 64KB random requests (1GB in total) Throughput Simulation Testbed Testbed Delay READ WRITE

  16. Impact of TCP Parameters • Impact of minimum timeout value (minrto) • Real RTT is roughly 1.5ms • A more precise configuration of timeout value in LAN is useful, and is possible Throughput # of Fast Retransmission # of Timeout 1s minrto 100ms minrto 10ms minrto 1ms minrto

  17. 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

  18. Future Works • Congestion point detection • better monitoring point? • more complicated cross traffic • Simulation: • More verification on write operations • Bursty Drop Model • More realistic system and disk model • More analysis on how TCP will affect the performance?

  19. 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?

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