R&M Data Center Handbook

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3.6.1. Introduction to Active Components
Small teams that want to exchange files with one another through their workstations have needs that are different
than those of large organizations, in which thousands of users must access specific databases. It is for that
reason that a distinction is made between so-called client/server networks, in which central host computers
(servers) are made available, and peer-to-peer networks, in which individual computers (clients) have equal rights
to release and use resources.
• In general, a Client/Server network differentiates between two types of computers that make up the
network: The server, as host, is a computer which provides resources and functions to individual users
from a central location; the client, as customer, takes advantage of these services. The services provided
by servers are quite diverse: They range from simple file servers which distribute files over the network or
release disk space for other uses, to printer servers, mail servers and other communication servers, up to
specialized services like database or application servers.
• As its name implies, a Peer-to-Peer Network consists principally of workstations with equal rights. Every
user is able to release the resources from his/her own computer to other users in the network. This
means that all computers in the network, to a certain extent, provide server services. In turn, this also
means that data cannot be stored in one central location.
In practice, however, hybrids of these network types are encountered more frequently than pure client/server- or
absolute peer-to-peer networks. For example, one could imagine the following situation in a company:
Tasks like direct communication (e-mail), Internet access (through a proxy server or a router) or solutions for data
backup are made available by means of central servers; and by contrast, access to files within departments or to
colleague’s printer within an office are controlled through peer-to-peer processes that bypass servers.
In a stricter sense, it is actually special software components, rather than specific computers, that are designated
as “clients” or “servers”.
This also results in differences in active network components for small and large organizations. Functions that are
provided must satisfy different requirements, whether these concern security (downtime, access, monitoring),
performance (modular expandability), connection technology (supported protocols and media) and other specific
functions that are desired or required.
3.6.2. IT Infrastructure Basics (Server and Storage Systems)
Active components, if they are network-compatible, have LAN interfaces of various types. These are specified by
the technology used for the transmission (transmission protocol, e.g. Ethernet), speed (100 Mbit/s, 1/10 Gbit/s),
media support (MM/SM, copper/fiber) and interface for the physical connection (RJ45, LC, etc.).
There are two types of latencies (delay) in the transmission of data for network-compatible devices:
• Transfer delay (in µs/ns, based upon medium and distance)
• Switching delay (in ms/µs, based upon device function, switching/routing)
One must therefore pay special attention to the latency of active components to ensure that the delay in the data
communication is as low as possible. This does not imply, however, that cabling quality does not have an effect on
data transmission.
On the contrary: Other factors like crosstalk, attenuation, RL, etc. play an important role in a clean signal
transmission. In addition, distances between signals are becoming smaller as a result of continually growing
transmission rates and other factors, while signal levels are becoming smaller as a result of enhanced modulation
types. Therefore, transmissions are becoming more susceptible to interference, i.e. transmissions are becoming
more sensitive to outside influences. In addition, performance reserves which can stand up to future data rates are
in demand more and more for cabling components.
In the final analysis, the typical investment period for cabling extends to over 10 years, as compared to 2 to 3
years for active components. Wanting to save costs in data center cabling would therefore certainly be the wrong
investment approach, especially since the percentage of this investment to total investments for a data center is
very small (5 % to 7 %) In addition, having to replace cabling is tied to enormous expenditure and, in the case of
switches for example, leads to a minor interruption in the data center if redundancy does not exist.
Decision makers must be aware here that the cabling structure in the data center, along with all of its components,
represents the basis of all forms of communication (e-mail, VOIP, etc.) – for a long period of time!
R&M Data Center Handbook V2.0 © 08/2011 Reichle & De-Massari AG Page 79 of 156