Specifications

Escala Tower PL & S, E, T System Hardware
Chapter 3: External Storage and SAN Subsystems 74/116
9es3s1c3.doc
Rev 5.9
02/12/2003
6. Storage Area Network (SAN) Introduction
The term SAN designates a new type of storage architecture in which the storage systems are attached
to a high-speed network dedicated exclusively to storage. It involves a whole new network totally
distinct of the existing communication networks, as described in the next figure. The application
servers (usually UNIX or NT based) access to the storage resource through the SAN. The Applications
servers are offloaded of most of their local storage resources, which becomes managed separately from
servers, and are consolidated at the data center, site or enterprise level.
This SAN architecture is represented in the next figure.
Stora
g
e Area
Network
Stora
g
e subsystems
(disk and tapes)
Application
servers
LAN
SAN
Local Area
Network
Terminal and
servers
In the literature, the term SAN refers either to the high speed network infrastructure, or may cover the
whole storage architecture, including servers, storage subsystems and management software.
Fibre Channel is today the preferred technology to implement these SAN architectures. This
technology is open, widely accepted on the market, and is defined by ANSI standards. A SAN
infrastructure based on Fibre Channel protocols supports multiple protocols, to simplify the migration
and integration of legacy equipment. For example, the infrastructure can convey SCSI protocols,
widely used in UNIX and Intel based servers, but also ESCON for IBM mainframes, and IP, to offer
some networking capabilities. But the SAN purpose is not to replace enterprise LANs. All these
protocols can use simultaneously the same cables.
This new storage architecture is very different from traditional architectures, where each storage
system is connected to a single or sometimes to a limited group of servers. That’s why they are
sometimes called “
private storage
” architectures. The SAN generates in the enterprises a revolution
similar to the one occasioned by the LAN deployment in the last decade. SANs deliver powerful
solutions which enable enterprises to manage their storage with an un-preceding efficiency and
flexibility. The benefits for the enterprise are the following: