FSx File Gateway performance over VPN

First, if you have not already tried accessing FSx Directly from your on-prem location, I would urge you to do so. Typically, if you are less than 1,000 miles away from the region, mapping clients to FSx directly performs well, and has added benefits of High Availability, reduced complexity (vs introducing a gateway), minimize on-prem footprint, reduced cost, among other things.

In regards to minimum bandwidth, we require 100 Mbps minimum between the Storage Gateway VM and AWS endpoints, this is for normal functions such as logs, metrics, and to be able to pull down updates. My recommendation would be to at least have 1 Gbps bandwidth for data traffic, and it really depends on the amount of data that will be sent back and forth between gateway and FSx. Using Site-to-Site VPN is fine, though internet latency can be high, variable and VPN does add some overhead, so Direct Connect would be the best option. We don't have any performance numbers published for these different types of scenarios, however I would strongly urge you to functionally test in your environment with significant load, and scale the number of clients. I would recommend keeping the client connection count below 100, the max is 500 but performance wildly varies when you add more users/connections.

If you have an account team, reach out to them and they can get you in touch with a specialist to review your use case, and advise on the correct solution for you.