July 14, KIMICS 2006 Kulveer Singh Graduate School of Design & IT Dongseo University Busan, South Korea Data Concurrency Issues in iSCSI Based-Data Storages

July 14, KIMICS 2006 Outline Introduction Concurrency Issues Hierarchical Locking System Design & Simulation Simulation Results Conclusion References

July 14, KIMICS 2006 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

July 14, KIMICS 2006 iSCSI stack Initiator : System which request block level data from Target Target : System which receive the SCSI commands from Initiator

July 14, KIMICS 2006 Main Reason For Concurrency No Centralized Locking mechanism implemented. No Cache consistency semantics used at the initiators.

July 14, KIMICS 2006 Concurrency Issue

July 14, KIMICS 2006 Design Approach

July 14, KIMICS 2006 Hierarchical Locking System * Indicates conflict S Share lock X Exclusive lock IS Intention Share IX Intention exclusive SXISIX S* * X**** IS* IX** Compatibility Table

July 14, KIMICS 2006 Central Metadata Manager (CMM) Lock Table consists of  Block ID  Conflict Count  Group Mode  Lock Queue  Wait Queue

July 14, KIMICS 2006 Ns2 (Network Simulator) Applications in Ns2 are virtual Does not transfer data. Packets are generated at transport layer by transport agent. Send at particular intervals according to the application specification.

July 14, KIMICS 2006 Simulation Model in Ns2 iscsiInitApp Agent iscsiRouterApp AgentiscsiTargetApp Agent Application Class iSCSI

July 14, KIMICS 2006 iSCSI layer implementation In Ns2 iSCSI layer on top of Full TCP agent iSCSI 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

July 14, KIMICS 2006 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

July 14, KIMICS 2006 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.

July 14, KIMICS 2006 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.

July 14, KIMICS 2006 Result of Varying Read/Write Access Pattern for LAN The parameters are  Number of LUN = 4  Allotted Time = 10  Directory Depth = 2

July 14, KIMICS 2006 Result of Varying Number of Initiators Sharing a LUN for LAN The parameters are  Read: Write Ratio = 60:40  Allotted Time =10  Directory Depth = 2

July 14, KIMICS 2006 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.

July 14, KIMICS 2006 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 [8] Ns by example – Jae Chung and Mark Claypool

July 14, KIMICS 2006 Questions?

July 14, KIMICS 2006 Thank You