Slow performance copying large file over network (scp)

Why you are using scp for copying large files in the first place? scp has its own overhead (encryption, authenticity checking, etc).

You can use rsync (rsync is very well suited for transferring large files over ssh because it is able to continue transfers that were interrupted due to some reason. Since it uses hash functions to detect equal file blocks the continue feature is quite robust.) or some other tool.

Please see this post. Copying large files over network , faster

If you want to use scp anyway , then you should use traceroute and tcpdump and iftopto see the packets from source to destination. May be you find something unusual.

Check to make sure -l option is not enabled to limit the bandwidth. Also, it looks like there is a -v will give insight to what is going on for the next run.

Verbose mode. Causes scp and ssh(1) to print debugging messages about their progress. This is helpful in debugging connection, authentication, and configuration problems.

This has been answered before. Quote from the answer.

scp is using interactive terminal in order to print that fancy progress bar. Printing that output to a file does not make sense at all, so scp detects when its output is redirected to somewhere else other than a terminal and does disable this output.

Full answer

https://stackoverflow.com/questions/3890809/bash-stdout-redirect-of-commands-like-scp

SCP man page

https://linux.die.net/man/1/scp