01-24-2016 07:46 AM
They are used for different purposes.
When you mirror the port you're usually in a troubleshooting mode and you want to collect 'raw' traffic traversing the port including payloads, headers and etc. Then you analyze it with a tool like Wireshark.
With sFlow or NetFlow you only send meta data, such as source/destination IPs, protocols being used, amount of data transferred and etc. You send it to your sFlow collector to build fancy graphs like Top interfaces per speed or Top protocols.
Have no figures about impact on 6450, but I can imagine port mirroring is more resource consuming comparing to sFlow.
Hope it helps.