I currently have a Raspberry Pi B+, running Raspbian, setup as an FTP-server (vsftpd). It receives 1 JPG image (about 30 kB) per s, saved to an NTFS-formatted USB HD, from my very basic IP camera, which can only handle classic FTP, hence vsftpd. I plan to expand this to a network of 5 cameras, so the Pi will handle 5 transactions per s, 30 kB each.
Now, I'm about to configure an OpenVPN server to allow remote viewing of the video streams from my cameras. I certainly don't want to just port forward to the cameras. The VPN will likely only see occasional traffic, perhaps a few minutes per day, but who knows, it might be more over time. Do you think the Raspberry Pi can handle the video over VPN and 5 FTP transactions/s simultaneously without any problems? I don't expect/need stellar VPN performance, but I want to avoid disruption of the FTP traffic.
I'm asking since I began this IP camera journey with the FTP server built into my Dovado PRO router, but during moderate to heavy general use of my internet connection (10/100 fiber) the FTP-server started to lag and sometimes the camera just gave up sending more images. That's why I separated the FTP function from the router with a Raspberry Pi. The Dovado router is, by the way, a decent performer with 700+ Mbit/s WAN-LAN throughput so I imagine it may be roughly on par with the Raspberry hardware.
I consider throwing in a second Raspberry Pi dedicated to running OpenVPN, but if I can manage very well with a single Pi handling FTP+OpenVPN, so much the better. Another solution would be a new router with, say, OpenWRT/Gargoyle and OpenVPN, but I'm really pleased with my Dovado regarding basic routing functionality.