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Investigating Serial Attached SCSI (SAS) over TCP (eSAS)and benchmarking eSAS prototype against legacy SAS

UCCS

Master’s Project Proposal

Deepti Reddy

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SCSI vs SASSCSI SAS

Topology Parallel Bus Serial Bus

Speed 3.2 Gbps 3 Gbps, 6Gbps, 12Gbps

Distance 1 to 12 meters 8 meters

Number of Targets

14 devices 128 expanders.> 16,000 with cascaded expanders

Devices SCSI only SAS & SATA

Connectivity Single Port Dual Port

Drive Form Factor

3.5” 2.5”

Cost Low Medium

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iSCSI & Related Work iSCSI protocol describes a means of transporting of the

SCSI packets over TCP/IP

The iSCSI specification is revised and updated by the Internet Engineering task Force (IEFT).

Work by S. Aiken, D. Grunwald, A. Pleszkun and J. Willeke shows the performance of a commercial iSCSI software implementation compared quite favorably with fibrechannel [7]

Security in iSCSI based network storage systems can degrade the performance of the syste. Research by S. Chaitanya, K. Butler, A. Sivasubramaniam, P. McDaniel and M. Vilayannur looks at methods to improve iSCSI performance [10]

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Typical SAS Topology

X X X

X

- DISK DRIVES

- EXPANDERS

DriverSAS CONTROLLER(HOST BUS ADAPTER)

~8m

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Motivation & Challenges

Overcome the distance and scalability limitations of traditional Serial Attached SCSI (SAS) by using eSAS.

Like iSCSI, eSAS takes advantage of existing internet infrastructure, internet management facilities as well as addresses distance limitations

Provide research results for future industry specification for eSAS and iSCSI.

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eSAS Topology

X

X

- DISK DRIVES

- EXPANDERS

MPT Driver

eSAS CONTROLLER/HBA

- TCP link

- SAS link

eSASHBA

Out of band SAS over TCP

In-band SAS

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eSAS Approach

The eSAS Request is initially sent by the eSAS Initiator to the eSAS Target over TCP.

The eSAS Target strips off the TCP header and sends the SAS frames using the SAS Initiator block on the eSAS Target to the SAS expander/drive.

The SAS expander/drive sends SAS frames to the eSAS Target.

Finally, the eSAS Target embeds the SAS frames received from the expander/drive over TCP and sends it to the eSAS Initiator.

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eSAS Message Format

The above shows how a legacy SAS header and data are embedded in an ethernet frame.

iSCSI uses the same approach where the SCSI header and data are encapsulated in an Ethernet frame.

Ethernet Header

IP Header

TCP Header

eSAS Header

eSASData

Ethernet Trailer

TCP Segment

IP Datagram

Ethernet Frame

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eSAS Approach

The above diagram shows a typical eSAS (SSP Read ) Request & Response sequence diagram.

iSCSI uses a similar approach where the back-end between the iSCSI target and SCSI drives uses the legacy SCSI protocol.

eSAS Request

eSAS Initiator

eSAS Target

SAS Expander

Open Address Frame

Open Accept

SAS Request Frame

Data Frame..

Data Frame

eSAS Response

Response Frame

Data Frame..

Data Frame

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Goals of the project

Design and develop a prototype of eSAS system−Write a client program using C/C++

that sends a set of eSAS commands to a server.

−Write a server program using C/C++ that receives a set of eSAS commands, processes them and responds to the client with eSAS responses.

Evaluate the eSAS solution and compare with legacy SAS.

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Tasks and Timeline

Task Timeline Status

Research SAS protocol

1.5 months Completed

Understand iSCSI at a high-level

15 days Completed

Investigate how to embed SAS traffic over TCP/IP

7 days Completed

Research how to benchmark SAS

10 days Ongoing (Expected Completion – November 22nd)

Proposal writing 7 days Completed

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Tasks and Timeline

Task Timeline Status

S/W development of the eSAS client mock up + S/W development of the eSAS server mock up using C/C++

~1.5 months Estimated Completion – January 10th

Final Project Report

15 days Estimated Completion – January 28th

Final Presentation + Defense

5 days Estimated Completion – January 31st

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Deliverables1. Research report on the design and

implementation of the client and server application

2. Research report on the benchmarking results of eSAS prototype app vs legacy

SAS.

3. The software client eSAS simulator developed for the project.

4. The software server eSAS simulator developed to test the client application

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References [1] T10/1760-D Information Technology – Serial Attached SCSI – 2 (SAS-2), T10, 18 April 2009, Available from http://www.t10.org/drafts.htm#SCSI3_SAS [2] Harry Mason, Serial attached SCSI Establishes its Position in the Enterprise, LSI Corporation, available from http://www.scsita.org/aboutscsi/sas/6GbpsSAS.pdf [3] J Satran, K Meth, C. Sapuntzakis, M. Chadalapka, E. Zeidner, RFC 3720 Internet Small Computer Systems Interface (iSCSI) Specification IETF, April 2004, available from http://www.ietf.org/rfc/rfc3720.txt [4] Cai, Y.; Fang, L.; Ratemo, R.; Liu, J.; Gross, K.; Kozma, M.; A test case for 3Gbps serial attached SCSI (SAS) Test Conference, 2005. Proceedings. ITC 2005. IEEE International, February 2006, available from http://ieeexplore.ieee.org/xpls/abs_all.jsp?arnumber=1584027  [5] Heng Liao, Tim Symons, Rachelle Tant, Managing Access Control Through Zoning, PMC-Sierra Inc., Spetember 2005, available from http://www.scsita.org/aboutscsi/sas/WP_PMC_Sierra_SAS_0905.pdf 

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References [6] Kalmath Meth, Julian Satran, Design of the iSCSI Protocol,Mass Storage Systems and Technologies, 2003. (MSST 2003). Proceedings. 20th IEEE/11th NASA Goddard Conference on Mass Storage Systems and Technologies, April 2003, available from http://ieeexplore.ieee.org/xpls/abs_all.jsp?arnumber=1194848&tag=1  [7] Stephen Aiken, Dirk Grunwald, Andrew R. Pleszkun, Jesse Willeke, A Performance Analysis of the iSCSI Protocol 20th IEEE/11th NASA Goddard Conference on Mass Storage Systems and Technologies, 2003, available from http://www.storageconference.org/2003/papers/20-Aikens-Performance.pdf  [8] M. Rajagopal, E. Rodriguez, R. Weber, RFC 3821 Fibre Channel over TCP/IP (FCIP) standard, IETF, July 2004, available from http://tools.ietf.org/html/rfc3821

[9] BLi Bigang, Shu Jiwu, Zheng Weimin, SCSI Target Simulator Based on FC and IP Protocols in TH-MSNS*

Department of Computer Science and Technology, Tsinghua University, Beijing China, 2005

 

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References [10] S. Chaitanya, K. Butler, A. Sivasubramaniam, P. McDaniel, M. Vilayannur,  Design, Implementation and Evaluation of Security in iSCSI-based Network Storage Systems, StorageSS '06 Proceedings of the second ACM workshop on Storage security and survivability, October 2006, available from http://portal.acm.org/citation.cfm?id=1179564