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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 - PowerPoint PPT Presentation
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iSCSI Performance in Integrated LAN/SAN Environment
Li Yin
U.C. Berkeley
Outline
Motivations Network Congestion and Disk Congestio
n 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 traf
fic
• Challenge:• How to sustain high I/O throughput even with competing
traffic?
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?
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, pack
et drop rate and etc.
Software Router
TargetInitiators
Experimental Setup iSCSI target disk is attached as raw device at the i
nitiator• 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
trtft TTR
irifi TTR
Read
Write
Ri
Ri
Rt
Rt
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
target
read write
No drop
1% drop
5% drop
Case 2: Disk Competition
Target machine continuously issue random I/O requests to the target disk
No network interference is introduced
Experimental Results
initiator
target
read write
No drop, No compete
4KB Competing Request
4MB Competing Requests
Result Analysis
read write
initiator
target
No drop, No Compete
4KB Competing Request
1% Drop
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 applicati
on.• 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)
READ WRITE
Throughput
Delay
Simulation
Testbed
Testbed
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
1s minrto 100ms minrto 10ms minrto 1ms minrto
Throughput # of Fast Retransmission # of Timeout
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• 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?
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?