Now that the power of 10GBASE-T transceivers is down to the point where high-port count switches and dual port NICs are enabled, pundits have moved to comparing the power of 10GBASE-T port to those of SFP+ direct-attach copper ports. This would be a fine comparison to make, if the usage models and utility were the same, but again, it’s all about utility and the applications.
SFP+ direct attach copper is more of a substitute for 10GBASE-CX4 than for to 10GBASE-T. It ably serves applications that require physically close and relatively low port-count 10Gigabit connectivity. Isolated clusters of high bandwidth are well served by SFP+ top-of-rack switching. SFP+ direct attach copper solves one of the problems that plagued 10GBASE-CX4 – replacing the bulky multi-lane twinax cabling with a single-lane serial connection, but still suffers from many of the utility drawbacks.
While 10GBASE-T allows the data center manager to flexibly floor-plan the room using structured cabling to interconnect units at a conveniently located patch panel distribution frame, utilizing the limited-reach SFP+ direct attach copper requires a data center manager to closely cluster the 10gigabit equipment in a less than 5 meter radius of the central switch (10m cable distance, minus 2.5m up and down each rack). This is just fine for small numbers of connections, the target market for 10GBASE-CX4, and for small-scale cluster computing 10gigabit deployments.
With high density switches, the result is a set of local rats-nests of point-to-point connectivity which can be difficult to manage. This is why you don’t see SFP+ passive copper pitched for larger end-of-rack switches. Applications which span large areas of data centers (or entire 10Gigabit data centers) will want to use their high port-count switches across the entire data center floor, and flexibly use them for all applications, including storage (iSCSI) and widely-deployed virtualization.
In contrast, equipment utilizing 10GBASE-T can be centrally reconfigured, regardless of where on the floor it physically fits. Equipment can be logically grouped and installed as space and maintenance demands allow, using existing practices. The utility of 10GBASE-T, allowing the use of existing practices for high density, is compelling.
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