Say No to scp
Why you should avoid scp over a WAN
In a Unix environment scp, sftp, and rsync are commonly used to copy data between hosts. While these tools work fine in a local environment, they perform poorly on a WAN. The openssh versions of scp and sftp have a built in 2 MB buffer that severely limits performance on a WAN. Even though rsync is not part of the openssh distribution, rsync typically uses ssh as transport and is therefore subject to the limitations imposed by the underlying ssh implementation. DO NOT USE THESE TOOLS if you need to transfer large data sets across a network path with a RTT 20ms (or greater).
The following results are typical: scp is 18x slower than single stream GridFTP, and 25x slower than parallel GridFTP.
Berkeley, CA to Argonne, IL (near Chicago).
RTT = 53 ms, network capacity = 10Gbps.
|HPN patched scp
|Globus, HTTP (e.g.:wget), 1 stream
|Globus, 4 streams
|8 Gbps (disk limited)
More information is here.