A Conceptual Overview of iSCSI

ManualsBrandsHP ManualsSoftwareHP-UX iSCSI (SCSI Over TCP/IP) Software

Executive Summary.........................................................................................................................................2

1. Introduction ..............................................................................................................................................2

2. Protocol Layering.....................................................................................................................................3

3. Hardware/Software Separation................................................................................................................4

4. Frame Construction .................................................................................................................................5

5. Network Entities and iSCSI nodes ...........................................................................................................6

6. Sessions and Connectivity.......................................................................................................................7

7. Portal Groups...........................................................................................................................................8

8. Bibliography .............................................................................................................................................9

9. Acronyms.................................................................................................................................................9

Summary of content (10 pages)

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A Conceptual Overview of iSCSI Executive Summary .........................................................................................................................................2 1. Introduction ..............................................................................................................................................2 2. Protocol Layering .....................................................................................................................................3 3.
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Executive Summary This White Paper provides a conceptual overview of iSCSI emphasizing the relationship of the iSCSI protocol to other computer subsystems. A basic understanding of mass storage and networking technologies is assumed. Concepts presented in this document include: • • • • • 1.
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“SCSI target”. iSCSI uses the phrases “iSCSI initiator” and “iSCSI target” as well. The term initiator or target is used without the protocol identifier when the protocol is not an issue. I/O operations from user or kernel applications are translated to the SCSI command set within the SCSI protocol layer. A SCSI mass storage transport maps the SCSI client-server protocol to a specific physical transport.
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At this point, the terminology may be getting a bit confusing. The confusion results from the use of 2 previously separate technologies (mass storage and networking) by a single subsystem (iSCSI). From a mass storage perspective, transport drivers such as Parallel SCSI, Fibre Channel, and iSCSI transmit SCSI operations. But for networking, the Transport Layer (TCP) is a layer of the network stack, not the mass storage transport driver.
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4. Frame Construction In section 2, “Protocol Layering”, an example of layering is provided that references the various levels of encapsulation. An Ethernet frame is depicted in Figure 3. Figure 3. Layout of an Ethernet Frame Ethernet Header IP Header TCP Header TCP Data Segment Ethernet Trailer TCP Segment IP Datagram Ethernet Frame Each layer of the network stack, TCP, IP, and the Physical and Data Link layer, provides its own encapsulation.
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There is a note of interest here for users of network protocol analyzers. Because there is no requirement that PDUs begin on a TCP Data Segment boundary, it is possible that simply grabbing an Ethernet frame with a protocol analyzer may result in an incorrect interpretation. To determine the start of a PDU, the end of the previous PDU must be known.
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entity. The iSCSI node is independent of the network portals providing access. The iSCSI name uniquely identifies the iSCSI node. A single iSCSI node within a network entity may be accessed through multiple network portals on that network entity. An iSCSI node is identified by its worldwide unique name, and an iSCSI node is defined independent of the network portals on the network entity. A network portal for an iSCSI initiator node is identified by its IP address.
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Figure 6. Representation of an iSCSI Multi-Connection Session iSCSI Initiator Connections Session iSCSI Target Session Network Portals The individual connections of a session may go through a variety of network infrastructure components (network switches, routers, hubs, etc.). iSCSI is agnostic to the network infrastructure components. The connection endpoints are the IP address/TCP port number pairs that identify the network portals. 7.
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8. iSCSI Bibliography Internet Small Computer Systems Interface, Internet Engineering Task Force, http://www.ietf.org/rfc/rfc3720.txt?number=3720 SAM SCSI Architectural Model, Technical Committee T10, http://www.t10.org 9. Acronyms The following are acronyms used throughout this document.
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HP Manufacturing Part Number 5991-1186 © 2003 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. Nothing herein should be construed as constituting an additional warranty. HP shall not be liable for technical or editorial errors or omissions contained herein.