Allyn Romanow (Cisco) Internet-draft Jeff Mogul (Compaq) Expires: September 2002 Tom Talpey (NetApp) Stephen Bailey (Sandburst) RDMA over IP Problem Statement draft-romanow-rdma-over-ip-problem-statement-00.txt Status of this Memo This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC2026. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. Copyright Notice Copyright (C) The Internet Society (2002). All Rights Reserved. Abstract This draft describes the problem that copying in network I/O typically causes high system costs in end-hosts at high speeds. The problem is due to the high cost of memory bandwidth, and it can be substantially improved using "copy avoidance." The high overhead has prevented TCP/IP from being used as an interconnection network, and instead special purpose memory-to-memory fabrics have been developed and widely used. An IP-based solution, developed within the IETF, is desirable for interoperability of various network fabrics. It is also particularly important for the IETF to guide the standardization because interconnection technology will soon start to be used over the wide area in the Internet. Romanow, et al Expires September 2002 [Page 1] Internet-Draft RDMA over IP Problem Statement 21 Feb 2002 Table Of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . 2 2. The high cost of data movement operations in network I/O . 3 2.1. Copy avoidance improves processing overhead . . . . . . . 5 3. Memory bandwidth is the root cause of the problem . . . . 6 4. High copy overhead is problematic for many key Internet applications . . . . . . . . . . . . . . . . . . . . . . . 7 5. How remote direct memory access (RDMA) can solve this problem . . . . . . . . . . . . . . . . . . . . . . . . . 9 6. Why this problem is relevant for the IETF . . . . . . . . 11 7. Security Considerations . . . . . . . . . . . . . . . . . 12 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . 12 References . . . . . . . . . . . . . . . . . . . . . . . . 12 Author's Address . . . . . . . . . . . . . . . . . . . . . 16 Full Copyright Statement . . . . . . . . . . . . . . . . . 17 1. Introduction This draft considers the problem of high host processing overhead associated with network I/O that occurs under high speed conditions. This problem is often referred to as the "I/O bottleneck" [CT90]. More specifically, the source of high overhead that is of interest here is data movement operations-- copying. This issue is not be confused with TCP offload, which is not addressed here. High speed refers to conditions where the network link speed is high relative to the bandwidths of the host CPU and memory. With today's computer systems, one Gbits/s and over is considered high speed. High costs associated with copying is an issue primarily for large scale systems. Although smaller systems such as rack-mounted PCs and small workstations would benefit from a reduction in copying overhead, the benefit to smaller machines will be primarily in the next few years as they scale in the amount of bandwidth they handle. Today it is large system machines with high bandwidth feeds, usually multiprocessors and clusters, that are adversely affected from copying overhead. Examples of such machines include all varieties of servers: database servers, storage servers, application servers for transaction processing, for e-commerce, and web serving, content distribution, video distribution, backups, data mining and decision support, and scientific computing. These larger systems typically, though not exclusively, terminate local connections rather than just wide area network connections. They are often located in data centers and they carry corporate and Internet traffic. Increasing, large systems access storage over a Romanow, et al Expires September 2002 [Page 2] Internet-Draft RDMA over IP Problem Statement 21 Feb 2002 Storage Area Network (SAN) rather than using directly attached disks, and many SANs are IP-based. Note that such servers almost exclusively service many concurrent sessions (transport connections), which, in aggregate, are responsible for > 1 Gbits/s of communication. Nonetheless, the cost of copying overhead for a particular load is the same whether from few or many sessions. Because of high end-host processing overhead in current implementations, the TCP/IP protocol stack is not used for high speed transfer. Instead special purpose network fabrics using remote direct memory access (RDMA) have been developed and are widely used. RDMA is a technology that allows the network adapter, under control of the application, to place data directly into and out of application buffers. This capability is also referred to as "direct data placement". Examples of such interconnection fabrics include Fibre Channel [FIBRE] for block storage transfer, Virtual Interface Architecture [VI] for database clusters, Infiniband [IB], Compaq Servernet [SRVNET], Quadrix [QUAD] for System Area Networks. These link level technologies limit application scaling in both distance and size, meaning the number of nodes. This problem statement substantiates the claim that in network I/O processing, high overhead is caused from data movement operations, specifically copying; and that copy avoidance significantly decreases the processing overhead. It describes when and why the high processing overheads occur, explains why the overhead is problematic, and points out which applications are most affected. The draft also considers why this problem needs to be addressed by the IETF in particular. The I/O bottleneck, and the role of data movement operations, have been widely studied in research and industry over the last approximately 14 years, and we draw freely on these results. The problem was investigated when high speed meant 100 Mbits/s FDDI and Fast Ethernet; it was again of concern when ATM with 155 Mbits/s and 1 Gbits/s Ethernet were introduced. And now that 10 Gbits/s Ethernet is becoming available there is an upswing of activity in industry and research [DAFS, IB, VI, CGZ01, Ma02, MAF+02]. 2. The high cost of data movement operations in network I/O A wealth of data from research and industry shows that copying is responsible for substantial amounts of processing overhead. It further shows that even in carefully implemented systems, eliminating copies significantly reduces the overhead, as referenced below. Romanow, et al Expires September 2002 [Page 3] Internet-Draft RDMA over IP Problem Statement 21 Feb 2002 Clark et al. [CJRS89] in 1989 shows that TCP [Po81] overhead processing is attributable to both operating system costs such as interrupts, context switches, process management, buffer management, timer management, and to the costs associated with processing individual bytes, specifically computing the checksum and moving data in memory. They found moving data in memory is the more important of the costs, and their experiments show that memory bandwidth is the greatest source of limitation. In the data presented [CJRS89], 64% of the measured microsecond overheads was attributable to data touching operations, and 48% was accounted for by copying. The system measured Berkeley TCP on a Sun-3/60 using 1460 Byte Ethernet packets. In a well-implemented system, copying can occur between the network interface and the kernel, and between the kernel and application buffers - two copies, each of which is two memory bus crossings - for read and write. Although in certain circumstances it is possible to do better, usually two copies are required on receive. Subsequent work has consistently shown the same phenomenon as the earlier Clark study. A number of studies report results that data- touching operations, checksumming and data movement, dominate the processing costs for messages longer than 128 Bytes [BS96, CGY01, Ch96, CJRS89, DAPP93, KP96]. For smaller sized messages, per- packet overheads dominate [KP96, CGY01]. The percentage of overhead due to data-touching operations increases with packet size, since time spent on per-byte operations scales linearly with message size [KP96]. For example, Chu [Ch96] reported substantial per-byte latency costs as a percentage of total networking software costs for an MTU size packet on SPARCstation/20 running memory-to-memory TCP tests over networks with 3 different MTU sizes. The percentage of total software costs attributable to per-byte operations were: 1500 Byte Ethernet 18-25% 4352 Byte FDDI 35-50% 9180 Byte ATM 55-65% Although, many studies report results for data-touching operations including both checksumming and data movement together, much work has focused just on copying [BS96, B99, Ch96, TK95]. For example, [KP96] reports results that separate processing times for checksum from data movement operations. For 1500 Byte Ethernet size, 20% of total processing overhead time is attributable to copying. The study used 2 DECstations 5000/200 connected by an FDDI network. (In this study checksum accounts for 30% of the processing time.) Romanow, et al Expires September 2002 [Page 4] Internet-Draft RDMA over IP Problem Statement 21 Feb 2002 2.1. Copy avoidance improves processing overhead A number of studies show that eliminating copies substantially reduces overhead. For example, results from copy-avoidance in the IO-Lite system [PDZ99], which aimed at improving web server performance, show a throughput increase of 43% over an optimized web server, and 137% improvement over an Apache server. The system was implemented in a 4.4BSD derived UNIX kernel, and the experiments used a server system based on a 333MHz Pentium II PC connected to a switched 100 Mbits/s Fast Ethernet. There are many other examples where elimination of copying using a variety of different approaches showed significant improvement in system performance [CFF+94, DP93, EBBV95, KSZ95, TK95, Wa97]. We will discuss the results of one of these studies in detail in order to clarify the significant degree of improvement produced by copy avoidance [Ch02]. Recent work by Chase et al. [CGY01], measuring CPU utilization, shows that avoiding copies reduces CPU time spent on data access from 24% to 15% at 370 Mbits/s for a 32 KBytes MTU using a Compaq Professional Workstation and a Myrinet adapter [BCF+95]. This is an absolute improvement of 9% due to copy avoidance. The total CPU utilization was 35%, with data access accounting for 24%. Thus the relative importance of reducing copies is 26%. At 370 Mbits/s, the system is not very heavily loaded. The relative improvement in achievable bandwidth is 34%. This is the improvement we would see if copy avoidance were added when the machine was saturated by network I/O. Note that improvement from the optimization becomes more important if the overhead it targets is a larger share of the total cost. This is what happens if other sources of overhead, such as checksumming, are eliminated. In [CGY01], after removing checksum overhead, copy avoidance reduces CPU utilization from 26% to 10%. This is a 16% absolute reduction, a 61% relative reduction, and a 160% relative improvement in achievable bandwidth. In fact, today's NICs commonly offload the checksum, which removes the other source of per-byte overhead. They also coalesce interrupts to reduce per-packet costs. Thus, today copying costs account for a relatively larger part of CPU utilization than previously, and therefore relatively more benefit is to be gained in reducing them. (Of course this argument would be specious if the amount of overhead were insignificant, but it has been shown to be substantial.) Romanow, et al Expires September 2002 [Page 5] Internet-Draft RDMA over IP Problem Statement 21 Feb 2002 3. Memory bandwidth is the root cause of the problem Data movement operations are expensive because memory bandwidth is scarce relative to network bandwidth and CPU bandwidth [PAC+97]. This trend existed in the past and is expected to continue into the future [HP97, STREAM], especially in large multiprocessor systems. With copies crossing the bus twice per copy, network processing overhead is high whenever network bandwidth is large in comparison to CPU and memory bandwidths. Generally with today's end-systems, the effects are observable at network speeds over 1 Gbits/s. A common question is whether increase in CPU processing power alleviates the problem of high processing costs of network I/O. The answer is no, it is the memory bandwidth that is the issue. Faster CPUs do not help if the CPU spends most of its time waiting for memory [CGY01]. The widening gap between microprocessor performance and memory performance has long been a widely recognized and well-understood problem [PAC+97]. Hennessy [HP97] shows microprocessor performance grew from 1980-1998 at 60% per year, while the access time to DRAM improved at 10% per year, giving rise to an increasing "processor- memory performance gap". Another source of relevant data is the STREAM Benchmark Reference Information website which provides information on the STREAM benchmark [STREAM]. The benchmark is a simple synthetic benchmark program that measures sustainable memory bandwidth (in MBytes/s) and the corresponding computation rate for simple vector kernels measured in MFLOPS. The website tracks information on sustainable memory bandwidth for hundreds of machines and all major vendors. Results show measured system performance statistics. Processing performance from 1985-2001 increased at 50% per year on average, and sustainable memory bandwidth from 1975 to 2001 increased at 35% per year on average over all the systems measured. A similar 15% per year lead of processing bandwidth over memory bandwidth shows up in another statistic, machine balance [Mc95], a measure of the relative rate of CPU to memory bandwidth (FLOPS/cycle) / (sustained memory ops/cycle) [STREAM]. Network bandwidth has been increasing about 10-fold roughly every 8 years, which is a 40% per year growth rate. A typical example illustrates that the memory bandwidth compares unfavorably with link speed. The STREAM benchmark shows that a modern uniprocessor PC, for example the 1.2 GHz Athlon in 2001, Romanow, et al Expires September 2002 [Page 6] Internet-Draft RDMA over IP Problem Statement 21 Feb 2002 will move the data 3 times in doing a receive operation -- 1 for the NIC to deposit the data in memory, and 2 for the CPU to copy the data. With 1 GBytes/s of memory bandwidth, meaning one read or one write, the machine could handle approximately 2.67 Gbits/s of network bandwidth, one third the copy bandwidth. But this assumes 100% utilization, which is not possible, and more importantly the machine would be totally consumed! (A rule of thumb for databases is that 20% of the machine should be required to service I/O, leaving 80% for the database application. And, the less the better.) In 2001, 1 Gbits/s links were common. An application server may typically have two 1 Gbits/s connections - one connection backend to a storage server and one front-end, say for serving HTTP [FGM+99]. Thus the communications could use 2 Gbits/s. In our typical example, the machine could handle 2.7 Gbits/s at theoretical maximum while doing nothing else. This means that the machine basically could not keep up with the communication demands in 2001, and with the relative growth trends it make the situation worse. 4. High copy overhead is problematic for many key Internet applications If a significant portion of resources on an application machine is consumed in network I/O rather than in application processing, it makes it difficult for the application to scale - to handle more clients, to offer more services. Several years ago the most affected applications were streaming multimedia, parallel file systems, supercomputing on clusters [BS96]. In addition, today the applications that suffer from copying overhead are more central in Internet computing - they store, manage, and distribute the information of the Internet and the enterprise. They include database applications doing transaction processing, e-commerce, web serving, decision support, content distribution, video distribution, and backups. Clusters are typically used for this category of application, since they have advantages of availability and scalability. Today these applications, which provide and manage Internet and corporate information, are typically run in data centers that are organized into three logical tiers. One tier is typically web servers connecting to the WAN. The second tier is application servers that run the specific applications usually on more powerful machines, and the third tier is backend databases. Physically, the first two tiers - web server and application server - are usually combined [Pi01]. For example an e-commerce server communicates with a database server and with a customer site, or a content Romanow, et al Expires September 2002 [Page 7] Internet-Draft RDMA over IP Problem Statement 21 Feb 2002 distribution server connects to a server farm, or an OLTP server connects to a database and a customer site. When network I/O uses too much memory bandwidth, performance on network paths between tiers can suffer. (There might also be performance issues on SAN paths used either by the database tier or the application tier.) The high overhead from network-related memory copies diverts system resources from other application processing. It also can create bottlenecks that limit total system performance. There are a large and growing number of these application servers distributed throughout the Internet. In 1999 approximately 3.4 million server units were shipped, in 2000, 3.9 million units, and the estimated annual growth rate for 2000-2004 was 17 percent [Ne00, PA01]. There is high motivation to maximize the processing capacity of each CPU, as scaling by adding CPUs one way or another has drawbacks. For example, adding CPUs to a multiprocessor will not necessarily help, as a multiprocessor improves performance only when the memory bus has additional bandwidth to spare. Clustering can add additional complexity to handling the applications. In order to scale a cluster or multiprocessor system, one must proportionately scale the interconnect bandwidth. Interconnect bandwidth governs the performance of communication-intensive parallel applications; if this (often expressed in terms of "bisection bandwidth") is too low, adding additional processors cannot improve system throughput. Interconnect latency can also limit the performance of applications that frequently share data between processors. So, excessive overheads on network paths in a "scalable" system both can require the use of more processors than optimal, and can reduce the marginal utility of those additional processors. Copy avoidance scales a machine upwards by removing at least two- thirds the bus bandwidth load from the "very best" 1-copy (on receive) implementations, and removes at least 80% of the bandwidth overhead from the 2-copy implementations. An example showing poor performance with copies and improved scaling with copy avoidance is illustrative. The IO-Lite work [PDZ99] shows higher server throughput servicing more clients using a zero-copy system. In an experiment designed to mimic real world web conditions by simulating the effect of TCP WAN connections on the server, the performance of 3 servers was compared. One server Romanow, et al Expires September 2002 [Page 8] Internet-Draft RDMA over IP Problem Statement 21 Feb 2002 was Apache, another an optimized server called Flash, and the third the Flash server running IO-Lite, called Flash-Lite with zero copy. The measurement was of throughput in requests/second as a function of the number of slow background clients that could be served. As the table shows, Flash-Lite has better throughput, especially as the number of clients increases. Apache Flash Flash-Lite ------ ----- ---------- #Clients Thruput reqs/s Thruput Thruput 0 520 610 890 16 390 490 890 32 360 490 850 64 360 490 890 128 310 450 880 256 310 440 820 Traditional Web servers (which mostly send data and can keep most of their content in the file cache) are not the worst case for copy overhead. Web proxies (which often receive as much data as they send) and complex Web servers based on SANs or multi-tier systems will suffer more from copy overheads than in the example above. 5. How remote direct memory access (RDMA) can solve this problem RDMA is a technology that allows the network adapter, under control of the application, to place data directly into and out of application buffers. This capability is also referred to as "direct data placement". It reduces the need for data movement. RDMA has been used extensively in memory-to-memory networks, both in research and in industry, as referenced below. It is a simple solution that once implemented does not need to be constantly revised with OS and architectural changes. Also it can be used with any OS and machine architecture. There has been extensive investigation and experience with two main alternative approaches to eliminating data movement overhead, often along with improving other Operating System processing costs. In one approach, hardware and/or software changes within a single host reduce processing costs. In another approach, memory-to-memory networking [MAF+02], hosts communicate via information that allows them to reduce processing costs. As discussed below, research and industry experience has shown that copy avoidance techniques within the receiver processing path alone have proven to be problematic. Many implementations have Romanow, et al Expires September 2002 [Page 9] Internet-Draft RDMA over IP Problem Statement 21 Feb 2002 successfully achieved zero-copy transmit, but few have accomplished zero-copy receive. And those that have done so make strict alignment and no-touch requirements on the application, greatly reducing the portability and usefulness of the implementation. In contrast, experience has been very satisfactory with memory-to- memory systems that do direct data placement, eliminating copies by passing information between sender and receiver. Direct data placement is a single solution for zero-copy networking in both the transmit and receive paths. The single host approaches range from entirely new hardware and software architectures [KSZ95, Wa97] to new or modified software systems [BP96, Ch96, TK95, DP93, PDZ99]. In early work, one goal of the software approaches was to show that TCP could go faster with appropriate OS support [CJR89, CFF+94]. While this goal was achieved, further investigation and experience showed that, though possible to craft software solutions, specific system optimizations have been complex, fragile, extremely interdependent with other system parameters in complex ways, and often of only marginal improvement [CFF+94, CGY01, Ch96, DAPP93, KSZ95, PDZ99]. The network I/O system interacts with other aspects of the Operating System such as machine architecture and file I/O, and disk I/O [Br99, Ch96, DP93]. For example, the Solaris Zero-Copy TCP work [Ch96], which relies on page remapping, shows that the results are highly interdependent with other systems, such as the file system, and that the particular optimizations are specific for particular architectures, meaning for each variation in architecture optimizations must be re-crafted [Ch96]. A number of research projects and industry products have been based on the memory-to-memory approach to copy avoidance. These include U-Net [EBBV95], SHRIMP [BLA+94], Hamlyn [BJM+96], Infiniband [IB], Winsock Direct [Pi01]. Several memory-to-memory systems have been widely used and have generally been found to be robust, to have good performance, and to be relatively simple to implement. These include VI [VI], Myrinet [BCF+95], Quadrix [QUAD], Compaq/Tandem Servernet [SRVNET]. Networks based on these memory-to-memory architectures have been used widely in scientific applications and in data centers for block storage, file system access, and transaction processing. By exporting direct memory access "across the wire", applications may direct the network stack to manage all data directly from application buffers. A large and growing class of applications has Romanow, et al Expires September 2002 [Page 10] Internet-Draft RDMA over IP Problem Statement 21 Feb 2002 already emerged which takes advantage of such capabilities, including all the major databases, as well as file systems such as DAFS [DAFS} and network protocols such as Sockets Direct [SD]. 6. Why this problem is relevant for the IETF There are several reasons why this is issue is relevant for the IETF. Interoperability is one reason, and the others involve the convergence of interconnection network and WAN. Most interconnection technology has been proprietary, even when developed by multiple vendors. There have been interoperability problems even with standards such as SCSI and PCI. An IP approach developed in the IETF would allow a heterogeneous underlying fabric to be tied together by a single IP networking technology. This would allow for multiple vendor systems, underlying hardware interconnection fabrics that could change over time and remain interoperable, and for interoperation over multiple hardware technologies, such as 1 and 10 Gbits/s Ethernet. Traditionally interconnection technology has been developed in an electrical engineering domain, and networking technology has been developed in the IETF. These domains are now converging, as hardware designers increasingly adopt networking-based approaches, and in particular are building IP-based systems. Since the IETF represents the best networking expertise, it is desirable to have it guide the standardization work. The most compelling reason interconnection network technology is relevant for the IETF is that our experience suggests that inevitably, and soon, there will be an intermixing between "interconnect" networks and WAN/Internet networks. Although today IP-based interconnect traffic is in local clusters and within the data center, inevitably this traffic will "leak out" and will be seen over the wide area network, including the Internet. There is already pressure for distributed data centers in the metro domain. Data centers distributed over the WAN will add value, and therefore someone will do it. It would be better for the development of the Internet and for the IETF to guide the development of IP-based interconnection technology properly while it is still primarily in the local environment, rather than having to deal with the technology later as it emerges onto the Internet. Unfortunately if the IETF does not become involved in engineering an IP standard, it will not prevent such a set of protocols from being developed, only unfortunately the appropriate IETF networking expertise will not benefit them. Romanow, et al Expires September 2002 [Page 11] Internet-Draft RDMA over IP Problem Statement 21 Feb 2002 7. Security Considerations The problem of reducing copying overhead in high bandwidth transfers via one or more protocols does not suggest any new security concerns. As a layer properly atop Internet transport protocols, the protocol(s) will gain leverage from IPSec and other Internet security standards. When a solution is proposed, security will be addressed in detail for that particular solution. The immediate target systems are local, where traditionally security has been more treated in a more relaxed fashion. However, the fact that almost certainly high speed interconnects will run over the Internet, makes it especially important to get security right from the outset. This is another good reason for the IETF to guide the standardization. 8. Acknowledgements Jeff Chase generously provided many useful insights information. 9. References [BCF+95] N. J. Boden, D. Cohen, R. E. Felderman, A. E. Kulawik, C. L. Seitz, J. N. Seizovic, and W. Su. "Myrinet - A gigabit-per- second local-area network", IEEE Micro, February 1995 [BJM+96] G. Buzzard, D. Jacobson, M. Mackey, S. Marovich, J. Wilkes, "An implementation of the Hamlyn send-managed interface architecture", in Proceedings of the Second Symposium on Operating Systems Design and Implementation, USENIX Assoc., Oct. 1996 [BLA+94] M. A. Blumrich, K. Li, R. Alpert, C. Dubnicki, E. W. Felten, "A virtual memory mapped network interface for the SHRIMP multicomputer", in Proceedings of the 21st Annual Symposium on Computer Architecture, April 1994, pp. 142-153 [Br99] J. C. Brustoloni, "Interoperation of copy avoidance in network and file I/O", Proceedings of IEEE Infocom, 1999, pp. 534-542 [BS96] J. C. Brustoloni, P. Steenkiste, "Effects of buffering semantics on I/O performance", Proceedings OSDI'96, USENIX, Seattle, WA Oct. 1996, pp. 277-291 Romanow, et al Expires September 2002 [Page 12] Internet-Draft RDMA over IP Problem Statement 21 Feb 2002 [CFF+94] C-H Chang, D. Flower, J. Forecast, H. Gray, B. Hawe, A. Nadkarni, K. K. Ramakrishnan, U. Shikarpur, K. Wilde, "High- performance TCP/IP and UDP/IP networking in DEC OSF/1 for Alpha AXP", Proceedings of the 3rd IEEE Symposium on High Performance Distributed Computing, August 1994, pp. 36-42 [CGY01] J. S. Chase, A. J. Gallatin, and K. G. Yocum, "End system optimizations for high-speed TCP", IEEE Communications Magazine , Volume: 39, Issue: 4 , April 2001, pp 68-74. http://www.cs.duke.edu/ari/publications/end-system.{ps,pdf} [Ch96] H.K. Chu, "Zero-copy TCP in Solaris", Proc. of the USENIX 1996 Annual Technical Conference, San Diego, CA, Jan. 1996 [Ch02] Jeffrey Chase, Personal communication [CJRS89] D. D. Clark, V. Jacobson, J. Romkey, H. Salwen, "An analysis of TCP processing overhead", IEEE Communications Magazine, volume: 27, Issue: 6, June 1989, pp 23-29 [CT90] D. D. Clark, D. Tennenhouse, "Architectural considerations for a new generation of protocols", Proceedings of the ACM SIGCOMM Conference, 1990 [DAFS] Direct Access File System http://www.dafscollaborative.org http://www.ietf.org/internet-drafts/draft-wittle-dafs-00.txt [DAPP93] P. Druschel, M. B. Abbott, M. A. Pagels, L. L. Peterson, "Network subsystem design", IEEE Network, July 1993, pp. 8-17 [DP93] P. Druschel, L. L. Peterson, "Fbufs: a high-bandwidth cross- domain transfer facility", Proceedings of the 14th ACM symposium of Operating Systems Principles, Dec. 1993 [EBBV95] T. von Eicken, A. Basu, V. Buch, and W. Vogels, "U-Net: A user-level network interface for parallel and distributed computing", Proc. of the 15th ACM Symposium on Operating Systems Principles, Copper Mountain, Colorado, Dec. 3-6, 1995 Romanow, et al Expires September 2002 [Page 13] Internet-Draft RDMA over IP Problem Statement 21 Feb 2002 [FGM+99] R. Fielding, J. Gettys, J. Mogul, F. Frystyk, L. Masinter, P. Leach, T. Berners-Lee, "Hypertext Transfer Protocol - HTTP/1.1", RFC 2616, June 1999 [FIBRE] Fibre Channel Standard http://www.fibrechannel.com/technology/index.master.html [HP97] J. L. Hennessy, D. A. Patterson, Computer Organization and Design, 2nd Edition, San Francisco: Morgan Kaufmann Publishers, 1997 [IB] InfiniBand Architecture Specification, Volumes 1 and 2, Release 1.0.a. http://www.infinibandta.org [KP96] J. Kay, J. Pasquale, "Profiling and reducing processing overheads in TCP/IP", IEEE/ACM Transactions on Networking, Vol 4, No. 6, pp.817-828, Dec. 1996 [KSZ95] K. Kleinpaste, P. Steenkiste, B. Zill, "Software support for outboard buffering and checksumming", SIGCOMM'95 [Ma02] K. Magoutis, "Design and Implementation of a Direct Access File System (DAFS) Kernel Server for FreeBSD", in Proceedings of USENIX BSDCon 2002 Conference, San Franscisco, CA, February 11-14, 2002. [MAF+02] Kostas Magoutis, Salimah Addetia, Alexandra Fedorova, Margo I. Seltzer, Jeffrey S. Chase, Drew Gallatin, Richard Kisley, Rajiv Wickremesinghe, Eran Gabber, "Structure and Performance of the Direct Access File System (DAFS)", accepted for publication at the 2002 USENIX Annual Technical Conference, Monterey, CA, June 9-14, 2002. [Mc95] J. D. McCalpin, "A Survey of memory bandwidth and machine balance in current high performance computers", IEEE TCCA Newsletter, December 1995 [Ne00] A. Newman, "IDC report paints conflicted picture of server market circa 2004", ServerWatch, July 24, 2000 Romanow, et al Expires September 2002 [Page 14] Internet-Draft RDMA over IP Problem Statement 21 Feb 2002 http://serverwatch.internet.com/news/2000_07_24_a.html [Pa01] M. Pastore, "Server shipments for 2000 surpass those in 1999", ServerWatch, Feb. 7, 2001 http://serverwatch.internet.com/news/2001_02_07_a.html [PDZ99] V. S. Pai, P. Druschel, W. Zwaenepoel, "IO-Lite: a unified I/O buffering and caching system", Proc. of the 3rd Symposium on Operating Systems Design and Implementation, New Orleans, LA, Feb. 1999 [PAC+97] D. Patterson, T. Anderson, N. Cardwell, R. Fromm, K. Keeton, C. Kozyrakis, R. Thomas, K. Yelick , "A case for intelligient RAM: IRAM", IEEE Micro, April 1997 [Pi01] J. Pinkerton, "Winsock Direct: the value of System Area Networks". http://www.microsoft.com/windows2000/techinfo/ howitworks/communications/winsock.asp [Po81] Postel, J., "Transmission Control Protocol - DARPA Internet Program Protocol Specification", RFC 793, September 1981 [QUAD] Quadrix Solutions, http://www.quadrix.com [SD] Sockets Direct, [SRVNET] Compaq Servernet, http://nonstop.compaq.com/view.asp?PAGE=ServerNet [STREAM] The STREAM Benchmark Reference Information, http://www.cs.virginia.edu/stream/ [TK95] M. N. Thadani, Y. A. Khalidi, "An efficient zero-copy I/O framework for UNIX", Technical Report, SMLI TR-95-39, May 1995 [VI] Virtual Interface Architecture Specification Version 1.0. http://www.viarch.org/html/collateral/san_10.pdf Romanow, et al Expires September 2002 [Page 15] Internet-Draft RDMA over IP Problem Statement 21 Feb 2002 [Wa97] J. R. Walsh, "DART: Fast application-level networking via data-copy avoidance", IEEE Network, July/August 1997, pp. 28-38 Author's Address Allyn Romanow Cisco Systems, Inc. 170 W. Tasman Drive San Jose, CA 95134 USA Phone: +1 408 525 8836 Email: allyn@cisco.com Tom Talpey Network Appliance 375 Totten Pond Road Waltham, MA 02451 USA Phone: +1 781 768-5329 EMail: thomas.talpey@netapp.com Jeffrey C. Mogul Western Research Laboratory Compaq Computer Corporation 250 University Avenue Palo Alto, California, 94305 USA Phone: +1 650 617 3304 (email preferred) EMail: JeffMogul@acm.org Stephen Bailey Sandburst Corporation 600 Federal Street Andover, MA 01810 USA Phone: +1 978 689 1614 Email: steph@sandburst.com Romanow, et al Expires September 2002 [Page 16] Internet-Draft RDMA over IP Problem Statement 21 Feb 2002 Full Copyright Statement Copyright (C) The Internet Society (2002). All Rights Reserved. This document and translations of it may be copied and furnished to others, and derivative works that comment on or otherwise explain it or assist in its implementation may be prepared, copied, published and distributed, in whole or in part, without restriction of any kind, provided that the above copyright notice and this paragraph are included on all such copies and derivative works. However, this document itself may not be modified in any way, such as by removing the copyright notice or references to the Internet Society or other Internet organizations, except as needed for the purpose of developing Internet standards in which case the procedures for copyrights defined in the Internet Standards process must be followed, or as required to translate it into languages other than English. The limited permissions granted above are perpetual and will not be revoked by the Internet Society or its successors or assigns. This document and the information contained herein is provided on an "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. Romanow, et al Expires September 2002 [Page 17]