July 14, 2006 1KIMICS 2006

Kulveer Singh Graduate School of Design & IT

Dongseo University Busan, South Korea

Data Concurrency Issues in iSCSI Based-Data Storages

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Outline

Introduction

Concurrency Issues

Hierarchical Locking System

Design & Simulation

Simulation Results

Conclusion

References

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iSCSI Defined: What Is iSCSI? iSCSI = internet Small Computer System Interface An interconnect protocol that:

Is designed for storage area networks (SANs) Supports the block-based storage needs of database applications Is TCP/IP based Establishes and manages connections between IP-based storage devices, hosts

and clients Is based on familiar and ubiquitous open standards Provides advanced IP routing, management, and security tools

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iSCSI stack

Initiator : System which request block level data from TargetTarget : System which receive the SCSI

commands from Initiator

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Main Reason For Concurrency

No Centralized Locking mechanism implemented.No Cache consistency semantics used at the initiators.

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Concurrency Issue

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Design Approach

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Hierarchical Locking System

* Indicates conflict• S Share lock• X Exclusive lock• IS Intention Share• IX Intention exclusive

S X IS IX

S * *

X * * * *

IS *

IX * *

Compatibility Table

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Central Metadata Manager (CMM)

Lock Table consists of Block ID Conflict Count Group Mode Lock Queue Wait Queue

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Ns2 (Network Simulator)

Applications in Ns2 are virtualDoes not transfer data.Packets are generated at transport layer by transport agent.Send at particular intervals according to the application specification.

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Simulation Model in Ns2

iscsiInitApp Agent iscsiRouterApp Agent iscsiTargetApp Agent

Application Class

iSCSI

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iSCSI layer implementation In Ns2

iSCSI layer on top of Full TCP agentiSCSI layer will be able to send data according to the user requirement.iSCSI layer composed of user interface layer and iSCSI agent.

iSCSI agent

User Interface

iSCSI layer

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Layer architecture In NS

iSCSI layer

Agent Wrapper(Full TCP agent)

TCP base class

Process_data(PDU)

Send_data (PDU)

Recv. (bytes)Send (bytes)

Packets

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Initiator & Target Simulation

Initiator will use the same layer architecture defined above.Target (iSCSI router) will also use the same architecture except the user interface layer will be eliminated from iSCSI layer.

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Simulation Parameters

Read/Write Access Pattern.Number of initiators sharing a LUN (Logical Unit Number).Allotted Time for the Exclusive Locks.Directory Depth.

Throughput Measured as the average number of locks granted

per initiator per minute by the CMM.

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Result of Varying Read/Write Access Pattern for LAN

0.0

10.0

20.0

30.0

40.0

50.0

60.0

70.0

80.0

Thro

ughp

ut/m

in

30 40 50 60 65 70 75 80 85 90Read Percentage

Effect of Read/Write Ratio on Avg. Throughput

Write Throughput Throughput Read Throughput

The parameters are Number of LUN = 4 Allotted Time = 10 Directory Depth = 2

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Result of Varying Number of Initiators Sharing a LUN for LAN

0.0

20.0

40.0

60.0

80.0

100.0

120.0

140.0

160.0

180.0

200.0

2 3 4 5 6 7 8# of Initiators

Effect of # of Initiators on Avg. Throughput

Write Throughput Throughput Read Throughput

The parameters are Read: Write Ratio = 60:40 Allotted Time =10 Directory Depth = 2

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Conclusion

Design has been validated by the NS2 simulator and the study of various parameters has been done.

Now the design can be practically implemented on the iSCSI router and performance can be measured practically.

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References

[1] Simulation of Hierarchical Locking Scheme for ISCSI SAN File Sharing – A Plan B report by Fang Zhang

[2] Caching in the Sprite Network File System - Michael N. Nelson, et al.[3] Metadata Update Performance in File Systems - Gregory R. Ganger and Yale N. Patt[4] Scalable Session Locking for a Distributed File System - Randal C. Burns, et al.[5] An Overview of the Global File System - He and Qing Yang.[6] The Linux Virtual File-system Layer - Neil Brown, et al.[7] The Network Simulator - Ns-2 http://www.isi.edu/nsnam/ns/[8] Ns by example – Jae Chung and Mark Claypool http://nile.wpi.edu/NS/

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Questions?

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Thank You

kulveer@dongseo.ac.kr