Re: scp troughput

[Greg Troxel <gdt%lexort.com@localhost>]

Edgar Fuß <ef%math.uni-bonn.de@localhost> writes:

> I just observed that scp throughput between my NetBSD machines stalls at some 
> 20 MB/s. Raw troughput (iperf) is up to 800 Mbit/s. CPUs are nowhere near 
> saturated. The weird thing it always saturates at nearly the exact same 
> level independent of hardware and file size.
>
> If I scp to a Debian machine, I get 65 MB/s, CPU bound on the receiving side.
> Debian->NetBSD is slow, Debian->Debian is fast.

Check your ssh config about whether you are trying to do compression.
Keep in mind that scp may reuse another connection if you have
ControlMaster set up.

Another thing to look at is socket buffer sizes.

I am guessing you have GbE wired, so you have < 1ms round-trip ping
times; I'm seeing 0.330 ms ping times even with a  2014 box and a 2008
laptop.

Normally, I recommend that people capture tcpdump traces and use the
scripts in the xplot package to visualize the TCP behavior. That's a
little involved and they have not kept up with tcpdump format changes.
xplot-devel is the best best.

I am seeing 12 MB/s myself, and looking into it.  On the same link, with
the equivalent of ttcp, I am seeing 69 MB/s (553 Mb/s), which seems
perhaps ok for a 2008 notebook with msk(4).