I've been curious on the real-world throughput of a directly attached Thunderbolt RAID vs a 10GB (single or bonded) Synology NAS. It's annoying to have to go to my desk to connect to the USB-C Drobo, and I have to jump ship sooner or later.
I have gone down this path myself for doing 8k editing. TB3 attached SSDs IO to my Mac at about 3GB/s. The ones on my server connected over 10GB fiber Ethernet actually only reach about 800MB/s and I suspect that that macOS networking stack is just not at all optimized for 10G.
10GBit networking is really only 1.25GBytes per second, so 800MBytes/s isn't saturating the link, but is 64% of the way there. TB3 has a theoretical throughput of 40GByte/s so 3GByte/s => 24GBit/s is 60%. Realistically both are lower to the theretical link performance than I would have guessed, so there may be some bottlenecks involved beyond just computational overhead, but it makes sense TB3 was going to win assuming the storage had the bandwidth.
To prevent causing issues upstream you would want to write to a fast NVME SSD first before backing up to a HDD array. Unfortunately, it doesn't support this use case as the NAS is designed for movie streaming, offices, security cameras etc.
Does anyone have better ideas?