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Investigating Serial Attached SCSI (SAS) over TCP ( tSAS )

Investigating Serial Attached SCSI (SAS) over TCP ( tSAS ). UCCS Master’s Project Deepti Reddy. SCSI vs SAS. SCSI (Small Computer System Interface) The SCSI protocol is an application layer storage protocol.  

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Investigating Serial Attached SCSI (SAS) over TCP ( tSAS )

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  1. Investigating Serial Attached SCSI (SAS) over TCP (tSAS) UCCS Master’s Project Deepti Reddy

  2. SCSI vs SAS SCSI (Small Computer System Interface) • The SCSI protocol is an application layer storage protocol.   • It's a standard for connecting peripherals to your computer via a standard hardware interface, which uses standard SCSI commands. SAS (Serial Attached SCSI) • SAS is the successor of SCSI technology • Initially introduced at 3Gb/s in 2004 • Currently, supports 6Gb/s • 12Gbps by 2012 • Significantly increased the available bandwidth offered by legacy SCSI storage systems. • Use of expanders increases the scalability over legacy SCSI

  3. SCSI vs SAS Comparing SCSI and SAS

  4. iSCSI 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] iSCSI protocol layering model

  5. Typical SAS Topology Driver SAS CONTROLLER (HOST BUS ADAPTER) ~8m X X X - DISK DRIVES - EXPANDERS X

  6. Motivation & Challenges • Overcome the distance and scalability limitations of traditional Serial Attached SCSI (SAS) by using tSAS. • Like iSCSI, tSAS takes advantage of existing internet infrastructure, internet management facilities as well as addresses distance limitations • Provide research results for future industry specification for tSAS and iSCSI.

  7. tSAS Topology SCSI Driver tSAS HBA SCSI Driver tSAS CONTROLLER/HBA X - TCP link - DISK DRIVES - SAS link X - EXPANDERS

  8. tSAS Topology SCSI Driver tSAS HBA SCSI Driver tSAS CONTROLLER/HBA X - TCP link - DISK DRIVES - SAS link X - EXPANDERS

  9. Goals of the project • Investigate how tSAS can be implemented • Design and develop a mock tSAS application • Write a client program using C/C++ that sends a set of tSAS commands to a server. • Write a server program using C/C++ that receives a set of tSAS commands, processes them and responds to the client with tSAS responses. • Evaluate the tSAS solution and compare with a mock iSCSI client/server application.

  10. Software and Hardware solutions for tSAS implementations • Software based tSAS solution • Cheaper than a hardware based solution • All tSAS processing is done by the processor and TCP/IP operations are also executed by the CPU • NIC is merely an interface to the network • TCP offload engine solution • NICs with integrated TOEs have hardware built into the card that allows the TCP/IP processing to be done at the interface • Hardware based tSAS solution • In a hardware-based tSAS environment, the initiator and target machines contain a host bus adapter (HBA) that is responsible for both TCP/IP and tSAS processing

  11. tSAS Approach • The tSAS Request is initially sent by the tSAS Initiator to the tSAS Target over TCP. • The tSAS Target strips off the TCP header and sends the SAS frames using the SAS Initiator block on the tSAS Target to the SAS expander/drive. • The SAS expander/drive sends SAS frames to the tSAS Target. • Finally, the tSAS Target embeds the SAS frames received from the expander/drive over TCP and sends it to the tSAS Initiator.

  12. tSAS 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 iSCSI header and data are encapsulated in an Ethernet frame. eSAS Data TCP Header Ethernet Header IP Header eSAS Header Ethernet Trailer TCP Segment IP Datagram Ethernet Frame

  13. tSAS Approach SAS Expander tSAS Target tSAS Initiator • The above diagram shows a typical tSAS (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. tSAS Request Open Address Frame Open Accept SAS Request Frame Data Frame . . Data Frame Data Frame . . Data Frame Response Frame tSAS Response

  14. tSAS Approach • Primitives • Primitives are special 8b/10b encoded characters that are used as frame delimiters, for out of band signaling, control sequencing in SAS • Most primitives can be conveniently ignored on the tSAS side except a few such as Broadcast primitives • SAS primitive can be encapsulated in an Ethernet frame • Discovery • Discovery in tSAS will be similar to SAS and will be accomplished by sending Serial management protocol (SMP) commands over TCP to the initiators and expanders downstream to learn the topology.

  15. tSAS Approach SMP Initiator Port on Expander SMP Target Port on Target Expander Client SMP Request Open Address Frame Open Accept SMP Request SMP Response Close SMP Response SMP Request & Response Sequence Diagram

  16. Test benches used for performance calculations • tSAS and iSCSI Mock Application • The client application and server application run on two different Windows machines/servers connected using a NetGearProSafe Gigabit Switch • Client makes Read/Write requests and the server processes and responds to requests made by the Client • Legacy SAS • A 6 GbpsSas Host Bus Adapter in a PCIe slot of a Super Micro server • A 6 Gbps SAS target connected to the Host Bus Adapter • IOMeter in Windows and VDBench in RHEL used to generate Read/Write IOs and measure performance • A SAS analyzer placed between the HBA and the SAS Target • Legacy iSCSI • Two windows machines/servers were used • On one machine the StarWindiSCSi Initiator was used • On another machine, the KernSafeiSCSi target software was used to create a iSCSI target • IOMeter was used to send Read/Write requests from the iSCSI Initiator to the iSCSI Target and measure performance • Wireshark used to capture Network Traffic

  17. tSASvsiSCSI Mock Application at 10 Mbps

  18. tSASvsiSCSI Mock Application at 100 Mbps

  19. tSASvsiSCSI Mock Application at 1 Gbps

  20. tSAS 512K Read at 10 Mbps, 100 Mbps and 1 Gbps

  21. Comparing tSAS mock application to legacy iSCSI and legacy SAS • tSAS results are extrapolated to 100 Gbps and so are the legacy iSCSI results to compare tSAS with legacy iSCSI • Assuming 100 Gbps connection rate performs 43.348 times better than 1 Gbps connection rates based on the 1 Gbps and 10 Gbps server scalability paper by NetApp where it is concluded that 10 Gbps performs 4.3348 times better than 1 Gbps. • These comparison results can’t be considered to be a fair comparison as the tSAS mock application is not a full fledged tSAS implementation • tSAS results are compared to legacy SAS • Legacy SAS performance results between the HBA and the SAS drive observed using the SAS analyzer for various transfer sizes under 2 MB show that Read/Write completions are < 1 ms.tSAS performs much slower than this at 100 Gbps • tSAS is compared to legacy SAS without including the delay at drive • These comparison results can’t be considered to be a fair comparison as the legacy SAS application is HBA based while the tSAS application is S/W based and is not a full fledged application

  22. Comparing tSAS mock application to legacy iSCSI

  23. Comparing tSAS Mock application to legacy SASX-Axis – Transfer Length (Bytes), Y-Axis – Time in Milliseconds

  24. Similar Work • Michael Ko’s patent on Serial Attached SCSI over Ethernet proposes a very similar solution to the tSAS solution provided in this project. • iSCSI specification (SCSI over TCP) itself is similar to a tSAS solution (SAS over TCP). The iSCSI solution can be heavily leveraged for a tSAS solution. • The Fibre Channel over TCP/IP specification also can be leveraged to design and implement a tSASsolution.

  25. Conclusion • tSAS is a viable solution • tSAS will be faster than a similar iSCSI implementation • Frame sizes in tSAS smaller than in iSCSI • Back-end of tSAS will be legacy SAS • tSAS should be visibly faster at larger transfer sizes • tSAS hardware solution would be the fastest vs a software solution • tSAS would perform better at smaller transfer sizes • tSAS will overcome the distance limitation of legacy SAS

  26. Future Work • More data points • The tSAS mock application can be run using a faster switch with connection rates greater than 1 Gbps to get more data points • Piggybacking • Response frames are piggybacked with the last DATA frame or a DATA frame is piggy backed with a request frame • Jumbo frames • Can be used to increase the amount of DATA that is passed from the initiator and target per Ethernet packet improving the performance results. • The Storage Associations can be motivated with similar work to fuel the conception of a tSASspecification • tSAS code can be implemented in a SAS HBA and performance can be measured using this direct implementation

  27. 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

  28. 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] BLiBigang, ShuJiwu, ZhengWeimin, SCSI Target Simulator Based on FC and IP Protocols in TH-MSNS* Department of Computer Science and Technology, Tsinghua University, Beijing China, 2005

  29. 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 [11] 1Gbps and 10Gbps Ethernet Server Scalability, NetApp, available fromhttp://partners.netapp.com/go/techontap/matl/downloads/redhat- neterion_10g.pdf [12] Michael A. Ko, LAYERING SERIAL ATTACHED SMALL COMPUTER SYSTEM INTERFACE (SAS) vOVERETHERNET, United States Patent Application 20080228897, 09/18/2008 available from http://www.faqs.org/patents/app/20080228897 [13] SCSI Primary Commands - 4 (SPC-4), Revision 31, T10, 2011/06/13, available from http://www.t10.org/members/w_spc4.htm

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