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HITE

APER

(cont.)

Doc Number

TC000602WP

N T R O D U C T I O N

The enterprise computing systems of many businesses were built around centralized, proprietary
computers, which are expensive to manage and upgrade. The networks that evolved around these
centralized systems use traditional network technologies such as Ethernet and TCP/IP, which are
designed for heterogeneous computing environments. Today, businesses can satisfy their
computing goals with a collection of low-cost, industry-standard servers distributed within a
cluster. A cluster is a group of two or more interconnected servers that act as a single computing
unit. Servers in a cluster can be physically distributed across various locations, yet to a user, the
cluster appears as a single, unified computing resource. In a parallel application cluster, for
example, each server simultaneously runs a copy of an application and the operating system. Client
requests are divided among the servers’ CPUs (central processing units), and the servers exchange
information about the portion of the client’s request they are processing. If one server fails, the
jobs it was processing are distributed across the remaining servers. Consequently, clustered servers
collectively generate tens of thousands of messages per second to keep track of the jobs they are
executing.

The high volume of server-to-server messaging in a cluster requires a very efficient software
communication interface and a highly reliable, high-speed, low-latency hardware interconnect.
Without an efficient server-to-server interconnect, the performance and scalability of a cluster is
severely limited. Traditional network technologies produce excessive software overhead, due to
their heterogeneous environments, and are too inefficient for intense server-to-server
communication. Therefore, in December 1997 Compaq and other industry leaders developed the
Virtual Interface (VI) Architecture specification for a distributed messaging interface that allows
more efficient server-to-server communication through a system area network (SAN). The VI
Architecture provides a common software and hardware interface standard so that customers can
choose the optimum SAN interconnect (Compaq

ServerNet II

, gigabit Ethernet, cLAN, ATM, or

others).

The Compaq

ServerNet II

SAN interconnect is the most complete industry-standard

implementation of the VI Architecture specification. Measurement of CPU utilization under
certain conditions shows that ServerNet II provides three times the performance of gigabit Ethernet
and TCP/IP. As a result, ServerNet II is quickly emerging as the interconnect of choice for
implementing clusters of industry-standard servers. Operating system vendor and independent
software vendor support for ServerNet II includes Windows 2000 Data Center, Windows 2000
Advanced Data Server, Linux, and SCO UnixWare 7.1.

R A D I T I O N A L

E T W O R K S V E R S U S

Y S T E M

R E A

E T W O R K S

Clustered servers can communicate with each other by using a traditional network or a SAN.
Traditional network technologies allow several different types of devices to communicate with each
other in complex, heterogeneous networks. Network applications manage communications
between the devices using multipoint protocols like TCP/IP and network interface controllers.
These protocols generate a large amount of software overhead (error checking and control
information) to ensure that messages are sent and received reliably. This software overhead
continually interrupts the servers’ CPUs. Consequently, the high volume of server-to-server
messaging in a cluster can overwhelm traditional network protocols like TCP/IP. In fact, clusters
that use traditional networks for messaging can lose as much as 20 to 30 percent of their capability
during intense messaging. This loss of system capability results in slower response times for users
and reduces the scalability, availability, and flexibility of clusters. When you consider the
unpredictable nature of Internet traffic, it becomes apparent that traditional network technologies
cannot handle server-to-server messaging in e-commerce environments.