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Why cabling matters

Storage area network managers have a lot of issues to consider, from what hardware and software to buy, to how they handle integration of different platforms, security and migration to new technologies. They also have to keep one eye on keeping management happy and juggling budgets, which are often subjected to cuts. Therefore, it is no surprise that with so many demands on their attention, some of the less ?glamorous' aspects of IT are often neglected.

 

Date: 1 Jan 2007

One such example is network cabling, a frequently overlooked areas of IT, yet one that can literally make or break the success of a storage area network. The problem is that network cabling is largely unseen once it is installed, and is not an everyday purchase. Does this matter? Yes it does, because most SAN managers do not deal with cabling issues often enough to become sufficiently expert in this area to make truly informed decisions. This means that they rely on the advice of consultants and installers, which can be dangerous. Although many of the specialist consultants and installers in this area are very reliable, mistakes are made and SAN managers leave themselves wide open to unscrupulous or insufficiently skilled third parties.

This is not just theory. I have been in the network cabling industry for two decades and during that time, I have seen examples where poor network cabling choices of installation quality have had a direct impact on the performance of a network. We have heard reports of cabling problems that have cost hundreds of thousands of pounds to correct. Since cabling runs beneath floors and within walls, it can be extremely time-consuming and laborious to put right. This is why 3M ? as a manufacturer of cabling components and systems ? puts so much emphasis on training and support for installers. Fortunately, most of the common problems we encounter can be avoided, as long as both the installer and the SAN manager are armed with the right information.

Given that few SAN managers will want to immerse themselves in the intricacies of cable installation and management, what are the key things they need to know when selecting cable type and installer?

Direct versus structured cabling


The first area to consider is whether to choose direct cabling or structured cabling. Direct cabling is generally cheaper and provides better protection against signal attenuation (loss in strength) than a series of connections within the link, unlike structured cabling, where each outlet is connected into a patch panel, which acts as a central control for the entire cabling system. Due to its comparatively low cost, direct cabling was traditionally been the choice of many SANs, but increasingly, more companies are now choosing structured cabling, because there are a whole host of other issues to consider.

For instance, unless a SAN is particularly small, it will require on-going management and this is much easier to control with structured cabling, since all connections are linked to a central panel, making it easier for the end user to see at a glance the current cabling configuration. The end user can make changes simply, by switching around the connection points and these can even be coloured-coded (as the case with the 3M system) for easier recognition. In other words, connections for different departments or service types can have different coloured connectors.

With direct cabling, it is extremely difficult and often impossible to make quick connection changes, particularly in large SAN installations where most of the cable is routed in floor or ceiling voids. Therefore, an installer has to be called in whenever a simple change needs to be made, unlike structured cabling, where end users can carry out most changes.

Any issues surrounding attenuation with structured cabling can be overcome by ensuring that the fibre terminations are of a high quality. The installation can be made even more robust by having all channels dual-pathed, with diverse routing of cables for redundancy, thereby minimising the impact of any cable failures.

By reducing the risk of failure or poor performance, as well as making on-going maintenance easier, many would argue that structured cabling is more economic in the long run. Vendor guarantees and test certificates from installers also give the customer an added level of assurance, while structured cabling standards provide very clear and precise set of guidelines for high quality installation. In all but the very smallest and simplest of installations, my recommendation would be structured cabling, but does it have any drawbacks of which the SAN manager should be aware?

Installation quality is crucial


The biggest issue is that structured cabling requires a higher level of skill from the installer and this is why SAN managers need to choose their provider carefully. Not all installers offer the same level of service, so it is important to choose a company that has been properly trained - and accredited by the vendors of the equipment it uses. Companies such as 3M provide extensive training courses of which installers can take advantage.

Derek Armer of Cooper Armer International Ltd, a structured cabling installation company that has provided the cabling systems for a number of SANs explains why structured cabling requires more skill. "When a patch-panel is being considered, all of the associated losses of connectors, splices and cables have to be included in the design for a particular operating speed. When choosing structured cabling, the first consideration is to establish the acceptable light loss budget for each fibre link, which in turn will depend on the required data speed for the current requirements, while remembering to build-in future-proofing."

Things that can go wrong include getting dust or dirt on the fibre connectors during installation, or misaligning fibre in the connector, both of which could lead to degradation in performance over time, or even a complete cable failure. This is why Derek Armer prefers to use connectors that incorporate dust covers, such as the 3M VF-45 range and which can be installed with minimal room for error.

Fibre better than copper


Due to its inherent high bandwidth and security benefits, optic cabling ? the de facto choice for SANs ? requires a higher level of installation skill that copper cabling, which is well suited to many to-the-desk applications. Therefore, it stands to reason that SAN managers are running a risk if they do not use installers who have considerable experience in fibre optic cabling. Many installers are generalists and for many applications, there is nothing wrong with using someone who is both an electrician and a communications installer, with experience mainly in copper connectivity. This is not the case with SANs, where fibre is really the only viable choice.

Fibre is virtually impossible to ?hack' into and also provides resistance to electro-magnetic interference (EMI), which is why it is used by banks and by military establishments. While copper's capabilities are still being explored and extended, in terms of sheer speed, fibre is in a league of its own. 10Gb Ethernet over copper may be a standard that will push back boundaries in to-the-desk environments, but it cannot compete with fibre in a SAN and customers should not be persuaded otherwise.

Standard changes


One development that SAN managers need to be aware of is the impending changes to the standards that govern structured cabling, due for introduction in 2007. The existing CENELEC EN 50173-1 standard is being expanded into five parts, with the base standard carrying all general requirements and then four proposed additional parts to cover: office cabling, industrial cabling, residential cabling and data centre cabling. This last part will also relate to SAN architecture.

The changes to the standard makes sense, because data centres and SANs are very different worlds to office environments, not least because there are far fewer user outlets, but many more connections to the external network. Also, data centres and SANs tend to require far greater capacity and robustness than most enterprise applications. The revised standard covers the very specific components and terms used within data centres and SANs, as well as addressing the fact that they have a particular kind of topography.

The access point to the external network is called the external network interface (ENI), and this is connected to a main distributor (MD) via a cabling sub-system. The zone distributor (ZD) allows access to the equipment outlets (EOs), either directly or via a local distribution point (LDP) to provide flexibility. Additional links are permitted between similar levels, for redundancy and flexibility. The storage units and servers will be connected to the EOs. The draft standard also addresses requirements to support longer distances found in data centres. For instance, maximum channel lengths are 300, 500 and 2000m for OM2/OM3 fibre and OS1 fibre.

However, it is not really necessary for SAN managers to be aware of all the details of the revised standard, just to make sure that the chosen installer is familiar with the new guidelines and has up-to-date training. After all, a SAN is a major investment for any organisation and prevention is always better than cure. This is why it makes sense to choose structured cabling, select vendor equipment that is reliable and straightforward to install, and to work with installers who have the right experience and training.

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