Will USB-C port dongle slow my external drive?

[yalag]

I bought the new imac without realizing that it doesn't have a thunderbolt 2 port. So my raid drive cant connect directly, I have to buy a dongle for usb-c. Is the dongle going to slow my external drive down?

 

[CWallace]

TB3 is fully backwards compatible with TB2, it will just run at TB2 speeds.

So you should see similar performance with the Thunderbolt 3 (USB-C) to Thunderbolt 2 Adapter as you did with the TB2 ports on the older iMac.