FileZilla Server Max Connections vs. Client Transfer Concurrency: Which Setting Best Mitigates Intermittent 421 Errors?

Goal: maintain reliable FileZilla Server availability during traffic bursts while avoiding intermittent "421" Too many connections responses.

Constraints: the server enforces a global maximum simultaneous connections (default 50) and per‑IP limits; exceeding these triggers "421" errors. The FileZilla Client can limit concurrent transfers, which reduces the rate at which new control and data connections are opened. Raising the server limit consumes additional CPU, memory, and file‑descriptor resources, whereas lowering the client limit may increase queue delay for many small files.

Should administrators increase the server's maximum simultaneous connections to accommodate peak client concurrency, or should they enforce a lower client‑side transfer limit to keep connection counts within the existing server threshold? What measurable indicators—such as CPU load, memory consumption, file‑descriptor usage, or observed connection counts—should guide the decision between adjusting server limits versus client concurrency settings?