Free tutors on Application and Management of Storage Networks (DEFINITION OF THE TERM ‘STORAGE NETWORK, Networks in the I/O path)

Free tutors on Application and Management of Storage Networks (DEFINITION OF THE TERM 'STORAGE NETWORK, Networks in the I/O path)

Application of Storage Networks

In the first part of the book we introduced the fundamental building blocks of storage networks such as disk subsystems, file systems, virtualization and transmission techniques. In the second part of the book our objective is to show how these building blocks can be combined in order to fulfil the requirements of IT systems such as flexibility, fault- tolerance and maintainability. As a prelude to the second part, this chapter discusses the fundamental requirements that are imposed independently of a particular application. First of all, Section 6.1 contrasts the characteristics of various kinds of networks in order to emphasize the shape of a storage network. Section 6.2 introduces various possibilities in the storage network for device sharing and data sharing among several servers. The final part of the chapter deals with the two fundamental requirements of IT systems: availability of data (fault-tolerance)

 DEFINITION OF THE TERM 'STORAGE NETWORK

In our experience, ambiguities regarding the definition of the various transmission techniques for storage networks crop up again and again. This section therefore illustrates

networks and storage networks once again from various points of view. It considers the layering of the various protocols and transmission techniques, discusses once again at which points in the I/O path networks can be implemented  and it again defines the terms LAN, MAN, WAN and SAN

Layering of the transmission techniques and protocols

If we greatly simplify the OSI reference model, then we can broadly divide the protocols for storage networks into three layers that build upon one another: transmission

techniques, transport protocols and application protocols (Figure 6.1). The transmission techniques provide the necessary physical connection between several end devices. Build-

ing upon these, transport protocols facilitate the data exchange between end devices via the underlying networks. Finally, the application protocols determine which type of data

the end participants exchange over the transport protocol. Transmission techniques represent the necessary prerequisite for data exchange between several participants. In addition to the already established Ethernet, the first part of the book introduces Fibre Channel and Infini-Band. They all define a medium (cable, radio frequency) and the encoding of data in the form of physical signals, which are transmitted over the medium. Transport protocols facilitate the exchange of data over a network. In addition to the

use of the tried and tested and omnipresent TCP protocol the first part of the book introduces Fibre Channel and the Virtual Interface Architecture (VIA). Transport proto-

cols can either be based directly upon a transmission technique such as, for example, Virtual Interfaces over Fibre Channel, Infini-Band or Ethernet or they can use an alter-

native transport protocol as a medium. Examples are Fibre Channel over IP (FCIP) and IP over Fibre Channel (IPFC). Additional confusion is caused by the fact that Fibre Channel defines both a transmission technique (FC-0, FC-1, FC-2) and a transport protocol (FC-2, FC-3) plus various application protocols (FC-4). Application protocols define the type of data that is transmitted over a transport protocol. With regard to storage networks we differentiate between block-oriented and file-oriented application protocols. SCSI is the mother of all block-oriented application protocols for block-oriented data transfer. All further block-oriented application protocols such as FCP, iFCP and iSCSI were derived from the SCSI protocol. File-oriented application protocols transmit files or file fragments. Examples of file-oriented application protocols discussed in this book are NFS, CIFS, FTP, HTTP and DAFS.

 Networks in the I/O path

The logical I/O path offers a second point of view for the definition of transmission techniques for storage networks. Figure 6.2 illustrates the logical I/O path from the disk

to the application and shows at which points in the I/O path networks can be used. Different application protocols are used depending upon location. The same transport

protocols and transmission techniques can be used regardless of this. Below the volume manager, block-oriented application protocols are used. Depending upon technique these are SCSI and SCSI offshoots such as FCP, iFCP and iSCSI. Today, block-oriented storage networks are found primarily between computers and storage sys- tems. However, within large disk subsystems too the SCSI cable is increasingly being replaced by a network transmission technique (Figure 6.3). Above the volume manager and file system, file-oriented application protocols are used. Here we find application protocols such as NFS, CIFS, HTTP, FTP and DAFS. In Chapter 4 three different fields of application for file-oriented application protocols were discussed: traditional file sharing, high-speed LAN file sharing and the World Wide Web. Shared disk file systems, which realize the network within the file system, should also be mentioned as a special case.