I was reading a white paper by Panduit2 that claims that 10GBaseT is suitable for use. I’ve been critical of Cat6A cable and believe that it’s not suitable for data centre use.
The problems that I have with 10GbaseT and Cat6a cabling are:
- High power consumption
- large physical Cat6A cable size
- poor mechanical properties of Cat6A copper
- Unreliability of copper in terms of Bit Error Rates (BER) and long term electrical capability.
It seems that Panduit has developed a special Cat6A cable that has a small cross section. And thus uses less space in the cable tray. However, the space is required to reduce crosstalk between pairs and Panduit would have to develop some technology to manage this. Likely this means a shield in the cable core which likely means expensive.
The early version of 10GBaseT used up to 25 watts of power per port. In the latest data sheets for Cisco Nexus 2232TM switches, Cisco states that 1W per port for 10GBaseT.
But what about the servers adapters ? The white paper is co-authored by Intel, Cisco and Panduit and states:
10GBASE-T power consumption has been rapidly dropping and now Intel’s third-generation 10GBASE-T adapter card, the dual-port Intel Ethernet Server Adapter X520-T2, which includes both Media Access Controller (MAC) and PHY, uses less than 10W per port.
So there server adapters still burn a lot of power, but getting less over time. Accepted.
Mechanical and Electrical Problems
This leaves the problems of mechanical and electrical performance over time. The basic problem I have is that Cat6A is close the limit of what can be achieved with copper in terms of electrical performance. It was originally believed that 10GBaseT wouldn’t even be possible.
The physical integrity of the Cat6A is vital to it’s propagation performance. Unlike Cat5, Cat6A has little room for signal degradation that can be caused by:
- cable kink will cause signal reflections
- over insertion of cable can cause degradation of connector performance
- physical cable weakness at the RJ45 connectors
I’m less concerned about the physical integrity of solid core copper cable in the horizontal, but I am concerned about the performance of multicore copper in the the rack from switch to server, and panel to switch. A simple accident where the Cat6A cable is pinched in a door, or crushed by a tool, can cause intermittent network problems that are truly hard to detect.
The EtherealMind View
I remain convinced that Fibre cabling is the future for 10Gigabit Ethernet and continue to recommend against 10GBaseT as a general rule. This paper doesn’t inspire me to change that view.
The purchase cost of Cat6A is already high and the price of high quality copper continues to appreciate, and the industry expects further price rises . The installation of Cat6A requires much more care, testing and validation to ensure that it works and this means even more installation cost (and a hidden cost at that). And remember, the underlying error rate of 10GBaseT is poor enough such that FCoE cannot use it (BER less tan 10^ -8 is not suitable for FibreChannel protocol). 1
I believe that customers should be advised to avoid 10GBaseT and implement OM3 fibre for all 10GBaseSX in your network. This will improve reliability, and you will sleep better at night.
- JDSU FCOE Blog – now deleted – for those who asked. ↩