How do you monitor and optimize the performance of SSH file transfer over LAN?

1 Choose the right tool

There are different tools and methods for transferring files over SSH, such as scp, sftp, rsync, and sshfs. Each tool has its own advantages and disadvantages, depending on the type, size, and number of files you want to transfer. For example, scp is simple and fast, but it does not support resume, compression, or synchronization. Rsync, on the other hand, can sync directories, compress data, and resume interrupted transfers, but it may be slower than scp for small files. You should choose the tool that best suits your needs and preferences.

2 Adjust the encryption settings

SSH uses encryption to secure the data transfer, but encryption also adds overhead and reduces the throughput. You can adjust the encryption settings to balance security and performance, depending on your network and file characteristics. For example, you can use a weaker cipher, such as arcfour or blowfish, instead of the default aes128-ctr, to reduce the CPU load and increase the speed. However, this may compromise the security of your data. You can also use the -C option with scp or rsync to enable compression, which can reduce the amount of data to be encrypted and transferred.

3 Monitor the network conditions

The performance of SSH file transfer also depends on the network conditions, such as latency, bandwidth, and congestion. You can use various tools and commands to monitor the network conditions and identify any issues that may affect the transfer speed. For example, you can use ping to measure the round-trip time between the source and destination hosts, iperf to measure the available bandwidth, and tcpdump or wireshark to analyze the network traffic and packets.

4 Tune the TCP parameters

SSH file transfer uses TCP as the underlying transport protocol, which means that it is subject to the TCP parameters and mechanisms, such as window size, congestion control, and retransmission. You can tune the TCP parameters to optimize the performance of SSH file transfer over LAN, depending on your network environment and requirements. For example, you can increase the TCP window size to allow more data to be sent without waiting for an acknowledgment, or you can disable or adjust the TCP congestion control algorithm to avoid unnecessary slowdowns.

5 Use parallel connections

Another way to improve the performance of SSH file transfer over LAN is to use parallel connections, which can leverage the available bandwidth and CPU resources more efficiently. Parallel connections can be especially useful when you need to transfer multiple files or directories, or when you have a high-latency network. You can use tools and options that support parallel connections, such as pscp or sftp with the -P option, or rsync with the -e option and a custom ssh command that uses the -o ControlMaster option.

6 Test and compare the results

Finally, you should test and compare the results of different tools, settings, and methods for SSH file transfer over LAN, to find the optimal combination for your scenario. You can use tools and commands that measure and report the transfer speed, such as scp or rsync with the -v option, or pv or dd with the -progress option. You can also use benchmarks and scripts that automate the testing process and generate reports, such as fio or ssh-perf.