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HP 226824-001 - ProLiant - ML750 Introduction Manual

Improving network performance
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RDMA protocol: improving network performance
technology brief
Abstract.............................................................................................................................................. 2
Introduction......................................................................................................................................... 2
Limitations of TCP/IP ............................................................................................................................ 2
RDMA solution .................................................................................................................................... 3
RDMA over TCP .................................................................................................................................. 4
RDMA protocol overview .................................................................................................................. 5
RDMA data transfer operations.......................................................................................................... 6
Send operations ........................................................................................................................... 6
RDMA write ................................................................................................................................. 7
RDMA read ................................................................................................................................. 7
Terminate .................................................................................................................................... 7
Verbs.............................................................................................................................................. 7
RNIC interface ................................................................................................................................. 8
RDMA over InfiniBand.......................................................................................................................... 9
InfiniBand RDMA protocols ............................................................................................................. 10
Direct Access Programming Library .............................................................................................. 10
Sockets Direct Protocol ................................................................................................................ 10
SCSI RDMA Protocol................................................................................................................... 11
InfiniBand link operation ................................................................................................................. 11
Conclusion........................................................................................................................................ 11
For more information.......................................................................................................................... 12
Call to action .................................................................................................................................... 12

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  Summary of Contents for HP 226824-001 - ProLiant - ML750

  • Page 1: Table Of Contents

    RDMA protocol: improving network performance technology brief Abstract.............................. 2 Introduction............................2 Limitations of TCP/IP ..........................2 RDMA solution ............................ 3 RDMA over TCP ..........................4 RDMA protocol overview ........................5 RDMA data transfer operations......................6 Send operations ........................... 6 RDMA write ..........................7 RDMA read ..........................
  • Page 2: Abstract

    Abstract Remote Direct Memory Access (RDMA) is a data exchange technology that improves network performance by streamlining data processing operations. This technology brief describes how RDMA can be applied to the two most common network interconnects, Ethernet and InfiniBand, to provide efficient throughput in the data center.
  • Page 3: Rdma Solution

    must be transferred in and out of memory several times (Figure 1): received data is written to the device driver buffer, copied into an operating system (OS) buffer, and then copied into application memory space. Figure 1. Typical flow of network data in receiving host Memory Chipset NOTE: The actual number of...
  • Page 4: Rdma Over Tcp

    RDMA over TCP Ethernet is the most prevalent network interconnect in use today. IT organizations have invested heavily in Ethernet technology and most are unwilling to tear out their networks and replace them. Reliance on Ethernet is justified by its low cost, backward compatibility, and consistent bandwidth upgrades over time.
  • Page 5: Rdma Protocol Overview

    RDMA protocol overview A series of protocols are layered to perform RDMA over TCP (Figure 3). The top three layers form the iWARP family of protocols that provide high-speed internet operability. The RDMA protocol converts RDMA write, RDMA read, and sends into Direct Data Placement (DDP) messages. The DDP protocol segments outbound DDP messages into one or more DDP segments, and reassembles one or more DDP segments into a DDP message.
  • Page 6: Rdma Data Transfer Operations

    DDP allows upper layer protocol (ULP) data, such as application messages or disk I/O, contained within DDP segments to be placed directly into its final destination in memory without processing by the ULP. This may occur even when the DDP segments arrive out of order. A DDP segment is the smallest unit of data transfer for the DDP protocol.
  • Page 7: Rdma Write

    The send with solicited event message is similar to the send message except that when the send with solicited event message has been placed and delivered, an event (for example, an interrupt) may be generated at the recipient, if the recipient is configured to generate such an event. This allows the recipient to control the amount of interrupt overhead it will encounter.
  • Page 8: Rnic Interface

    eliminate data copy operations, and significantly reduce communications overhead and latencies by allowing one verbs consumer to place information directly in the memory of another verbs consumer, while preserving operating system and memory protection semantics. Figure 4 is a conceptual model of elements used in RNIC operation, including privileged mode consumers, non-privileged mode consumers, RNIC components, and the RNIC interface.
  • Page 9: Rdma Over Infiniband

    RDMA over InfiniBand InfiniBand is a high-performance, low-latency alternative to Ethernet. InfiniBand architecture uses a switched-fabric, channel-based design that adapts well to distributed-computing environments where performance, infrastructure simplification, and convergence of component interconnects are key design goals. A data center employing an InfiniBand infrastructure is less complex and easier to manage.
  • Page 10: Infiniband Rdma Protocols

    InfiniBand uses a communications stack (Figure 6) that specifies both the functionality and physical connectivity of the channel adapter. Adapter functionality is defined by its verb set as detected by the application programming interface (API) of the operating system being used. Each layer is subservient to the layer preceding it and must complete its function before passing the responsibility on to the next layer.
  • Page 11: Scsi Rdma Protocol

    SCSI RDMA Protocol SCSI RDMA Protocol (SRP) encapsulates SCSI commands over InfiniBand for SAN networking. Operating from the kernel level, SRP allows SCSI commands to be copied between systems via RDMA for low-latency communications with storage systems. InfiniBand link operation Since some network devices can send data faster than the destination device can receive it, InfiniBand uses a queue pair (one send, one receive) system similar to the one for RDMA over TCP.
  • Page 12: For More Information

    For more information For more information on RDMA, go to the RDMA Consortium website at www.rdmaconsortium.org Call to action Send comments about this paper to: TechCom@HP.com. © 2006 Hewlett-Packard Development Company, L.P. The information contained herein is subject to change without notice. The only warranties for HP products and services are set forth in the express warranty statements accompanying such products and services.