R&M Data Center Handbook

www.datacenter.rdm.com
Summary
Despite the validity of cabling standards for data centers, it
must be assumed that a cabling system designed in accordance
with these standards will not necessarily ensure the
same usability period as required standards for office
cabling. Designs with a requirements-oriented cabling
system, and the modified design and material selection that
are derived from this, must not be described as incorrect.
They represent an alternative and may be a reasonable
option in smaller data centers or server rooms.
Data centers must be planned like a separate building
within a building, and a cabling system that is structured
and static therefore becomes more likely – at least between
distributors. In any event, planners must ensure that capacity
(in terms of transmission rate) is valued more than
flexibility. Quality connection technology must ensure that
fast changes and fast repairs are possible using standard
materials. This is the only way to be able to guarantee the
high availabilities that are required.
Data center planners and operators will also face the
question of whether using single mode glass fiber is still
strictly necessary. The performance level of the laseroptimized
multimode glass fibers available today already
open up numerous options for installation. The tables above
showed what potentials can be covered with the OM3 and
OM4 fibers. Do single-mode fibers therefore have to be
included in examinations of transmission rate and transmission
link
A criterion that may make single mode installations absolutely necessary is, for example, the length restriction for
OM3/OM4 from IEEE 802.3ba (40/100 GbE). The 150 meter limitation with OM4 fiber for 40/10 Gigabit Ethernet
would likely be exceeded in installations with extensive data center layouts. Outsourced units, like backup
systems stored in a separate building, could not be integrated at all. In this case, single mode is the only technical
option. A cost comparison is not necessary.
The high costs of transceivers for single mode transmission technology are a crucial factor in configurations that
can be used with either multimode or single mode. Experience shows that a single mode link costs three to four
times more than a multimode link. With multimode up to double the port density be achieved. However, highly
sophisticated parallel optic OM4 infrastructures also require considerable investments. The extent to which the
additional expenses are compensated through lower cabling costs (CWDM on single mode vs. parallel optic OM4
systems) can only be determined by an overall examination of the scenario in question. In addition, the comparably
higher energy consumption is also a factor. Single mode consumes about three to five times more watts
per port than multimode.
Whether one uses multimode length restrictions as a basis for a decision in favor of single mode depends upon
strategic considerations in addition to a cost comparison. Single mode offers a maximum of performance
reserves, in other words a guaranteed future beyond current standards. Planners who want to eliminate restricting
factors over multiple system generations and are willing to accept a bandwidth/length overkill in existing applications
should plan on using single mode.
3.10 Implementations and Analyses
The 40 GbE specification is geared to High-Performance Computing (HPC) and
storage devices, and is very well suited for the data center environment. It supports
servers, high-performance clusters, blade servers and storage networks (SAN).
The 100 GbE specification is focused on core network applications – switching,
routing, interconnecting data centers, Internet exchanges (Internet nodes) and
service provider Peering Points (PP). High-performance computing environments
with bandwidth-intensive applications like Video-on-Demand (VoD) will profit from
100 GbE technology. Since data center transmission links typically do not exceed
100 m, 40/100 GbE components will be significantly more economical than OS1
and OS2 single mode components, and still noticeably improve performance.
Page 124 of 156 © 08/2011 Reichle & De-Massari AG R&M Data Center Handbook V2.0