2.5 Networking behind the Server

As illustrated in Figure 2-11, storage area networks introduce network relationships behind the server. Replacing the dedicated parallel SCSI cabling bond between servers and storage with peer-to-peer networking does two things: It not only provides more flexibility in the deployment of storage resources but also frees storage from the exclusive ownership by a single server. In a SAN topology, any storage resource can be assigned to any server. Although these new relationships must be managed, SANs enable more efficient use of storage resources and lower administrative costs through storage consolidation.

Figure 2-11. A simple storage area network

graphics/02fig11.gif

SANs represent, after WANs and LANs, a third type of network. A SAN may be isolated from the mainstream messaging network through protocol segregation (Fibre Channel) or network segregation (virtual LAN, or VLAN). In either case, the purpose of the SAN is to provide high-performance access to shared storage resources using SCSI block transactions.

The SAN infrastructure has provided a foundation for new storage applications such as server clustering, LAN-free and server-free tape backup, and storage consolidation. To serve these, a new generation of storage applications, management platforms, and products has been developed. Along with that comes a market demand for people who have the skills to deploy and manage SAN environments.

With current technology, you can build the SAN infrastructure using Fibre Channel, Gigabit Ethernet, or a combination of both. Fibre Channel provides both 1Gbps and 2Gbps speeds and so offers an advantage in raw bandwidth for device attachment. Gigabit Ethernet provides 1Gbps for device attachment and 10Gbps for interswitch links, and it offers an advantage in ubiquity and relatively lower plumbing costs.

The combination of a high-speed network transport and native SCSI protocol results in an efficient means to deploy servers, disk arrays, and tape subsystems, and it frees all components from the constraints of parallel SCSI architecture. At the same time, the fusion of storage and networking has created new relationships that must be managed. If a storage resource on a SAN can be assigned to any server, it can also be inadvertently assigned to unintended servers. Concurrent with the development of SAN technology, new tools such as storage zoning, LUN masking, and storage virtualization are required to balance the productivity gains SANs provide with the disruptions they have created for traditional storage management.



Designing Storage Area Networks(c) A Practical Reference for Implementing Fibre Channel and IP SANs
Designing Storage Area Networks: A Practical Reference for Implementing Fibre Channel and IP SANs (2nd Edition)
ISBN: 0321136500
EAN: 2147483647
Year: 2003
Pages: 171
Authors: Tom Clark

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