We regularly have to transfer files between servers at high speed and got this problem when a single server is slower than the rest and they reside in 2 DCs next to each other. All other servers got around 500KB/sec, this one only got 170KB/sec. With some research, it turns out that using different options of scp can improve speed drastically. The new speed we got is around 1.3MB – 1.7MB/sec for all servers with compression & using a blowfish as the encryption method.
Before: scp -C -c blowfish -P [port] SRC DEST
After: scp -C -c blowfish -P [port] SRC DEST