Another article for the Root6 catalogueAs our need for higher speed data transfer increases and the advantages of shared storage become apparent to post-producers – high definition television places a requirement on disk space several times that of standard definition and big productions require editors to collaborate on shows. With all this in mind it is no surprise that we’re leaving SCSI behind and our Avids are increasingly using cheaper commodity-based FireWire storage for low-end DV-based work and fibre-channel for larger SAN (“Storage Area Network”)-based collaborative workflows. At Root6 we’ve seen an increase in SAN sales over the last year with Facilis’s Terrablock product line hitting the price/performance spot for many users.
With this as the background, we now do a significant amount of fibre installations as people look to future proof their facilities. The differences between traditional data fibre and the “young turks” who operate SANs, are significant and the lack of appreciation of those differences has caused many an installation gaff for integrators who haven’t taken the time to appreciate those details.
The biggest difference between data networks and “virtualised SCSI” is in the glass(!) – fibre channel works in a “multi-mode” – many frequencies of light are launched down the same glass fibre cable which will maintain data rates below 10 gbits per second over several hundred metres. Single mode fibre, which has longer been used for more traditional data applications – typically TCP/IP – uses a single colour laser and so the glass can be optimised for that “mode”. Data rates of fifty gigabits per second are achievable over tens of kilometres without amplification. These details are given but after that there are a few other considerations that make the difference between a working installation and a truly flexible/scalable one.
When you buy some fibre-channel storage the manufacturer will ship you patch cords that are commonly refered to as “tight-buffered” cable.
The glass fibres are lined in a nylon jacket which is coated in a plastic sheath. These cables are cheap to manufacture and are flexible enough for dressing within equipment bays. The problem with tight-buffered cable comes when you try and run long lengths of it through voids and dry-risers (between the machine room and the edit suite, for example) – it isn’t really man enough for the job and will often fail. Traditional cable-working techniques tend to compromise it, which is expensive if you have to hire wiring staff or worse still if you lose the edit because the cable has just given up the ghost during that important job. The attraction to most in-house engineering departments is that you can buy the cables ready-made and so you don’t have to concern yourself with manufacturing leads that you have little familiarity with.
By far the better way of providing a fibre infrastructure is to run in a “loose buffered” cable. The construction of this differs in that the fibres float in a mineral oil that is contained within a plastic hose. This is wound in a Kevlar mesh (the same material they make bullet-proof vests out of!) which is all covered in a plastic sheath. The cable scores over tight-buffered cable, in that the fibres can slide within the oil as the cable is pulled around bends and the Kevlar means you can step on the cable and abuse it a lot more than patch cord cable. The bulk of the cost of the cable is in the protective construction and not in the glass fibres themselves and so it becomes very economical to run in a four-core where you might only need two (a transmit-receive pair) or a twenty-four core where you only need eight (for example) – this price scalability means you can future proof yourself (you always end up building more edit suites!) and guard against possible damage (despite the glowing account above it does occasionally get damaged). Neither of these advantages can be ascribed to tight-buffered cable. Although the initial installation cost is marginally higher the total cost of ownership and reliability/flexibility is an order of magnitude better.
Root6 has invested in both training and the necessary equipment to offer a full fibre installation service and will be happy to advise when you are thinking of investing in a SAN. As an aside, in the eighteen months since we opened the fibre division we have not had to return to a client’s premises to repair a broken fibre – we have had to help out several other clients who’ve found that half of the pre-made tight-buffered cables they’ve had run in have failed very quickly.
Labels: articles, cable, networking
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