The effective speed, in theory, might be 20Gbps depending on how you set up your network adapter.
From the very get-go, the important thing is that the two ports of Chelsio T-520CR support link aggregation & fail-over features which are ideal for critical network applications that require redundancy, high-availability, and high throughput capabilities.
With 2 ports, you can use "link aggregation" or "bonding" which makes the 2 ports look just like 1 regular port to the applications you are running. There are pros and cons to this:
- Better theoretical speed (though you will be limited by the slowest part of your connection path)
- Better fault tolerance - this was the original intent of the technology
- Allows load balancing between 2 networks (E.g. cable + DSL)
- Your speed is still limited by the slower connection path. For instance, if your internet service provider is only giving you 10Gbps, you can't connect to the internet any faster than that by using 2 ports