scp more perfectly fills the pipe than NFS/TCP

Zaphod Beeblebrox zbeeble at
Sat Dec 19 05:47:57 UTC 2009

Here's an interesting conundrum.  I don't know what's different
between the TCP that scp uses from the TCP that NFS uses, but given
the same two FreeBSD machines, SCP fills the pipe with packets better.

Examine the following graphic:

The system doing the scp and the NFS server is FreeBSD-7.2-p1.  The
system receiving the scp and the NFS client is FreeBSD-8.0-p1

The scp transfer is the left hand side of the graph and the NFS
transfer is on the right.

The NFS is mounted with "-3 -T -b -l -i" and no other options.  Files
are being moved over NFS with the system "mv" command.  The files in
each case are large (50 to 500 meg files).

The connection is a DSL that terminates on the local lan near the
server (I own and run the DSL and the ISP)

In either case, the connection is lightly used by only me --- and I'm
fairly certain that this isn't another network factor at play.

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