iPerf3

Iperf is a tool for network performance measurement and tuning. It is a cross-platform tool that can produce standardized performance measurements for any network. Iperf has client and server functionality, and can create data streams to measure the throughput between the two ends in one or both directions.

here is a very good tutorial (french version)

https://www.forum-nas.fr/threads/tuto-utilisation-de-iperf3-avec-un-nas-qnap.19315/

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