[Bug 204409] Uploading to a FreeBSD sshd server drops bandwidth

bugzilla-noreply at freebsd.org bugzilla-noreply at freebsd.org
Mon Nov 9 23:12:56 UTC 2015


https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=204409

            Bug ID: 204409
           Summary: Uploading to a FreeBSD sshd server drops bandwidth
           Product: Base System
           Version: 10.2-RELEASE
          Hardware: Any
                OS: Any
            Status: New
          Severity: Affects Only Me
          Priority: ---
         Component: bin
          Assignee: freebsd-bugs at FreeBSD.org
          Reporter: vlad-fbsd at acheronmedia.com

It appears that UPLOADING to sshd (eg. scp localfile remote.tld:remotefile)
will happen at very limited bandwidth.

I haven't been able to isolate which circumstances those are precisely, but,
between two servers when the command is reversed (eg. scp remote.tld:remotefile
./localfile) the transfer happens at full available speed.

To make this clear, for a particular set of servers, for example:

on server A:
------------
scp localfile B:remotefile   ->   40Mbps  (upload to sshd)
scp B:remotefile localfile   ->  120Mbps  (download from sshd)

scp localfile B:remotefile   ->  200Mbps  (upload to sshd, Debian on B)
scp B:remotefile localfile   ->  120Mbps  (download from sshd, Debian on B)


on server B:
------------
scp localfile A:remotefile   ->   30Mbps  (upload to sshd)
scp A:remotefile localfile   ->  120Mbps  (download from sshd)

scp localfile A:remotefile   ->   40Mbps  (upload to sshd, Debian on B)
scp B:remotefile localfile   ->  200Mbps  (download from sshd, Debian on B)

NOTE: When upload is _TO_ FreeBSD sshd, the bandwidth is 30-40Mbps. 


Which means the differences between upload and download are not due to network
congestion or particular datacenter setup, whether a server is dedicated or
VPS, UFS2 filesystem or ZFS, 1GB of RAM or 16GB. Though all were 64bit. Tested
between Leaseweb Amsterdam, DigitalOcean Amsterdam, DigitalOcean Frankfurt,
Hetzner Germany (Falkenstein) and Rackspace in London.

This also affects rsync over ssh, so it's not just scp. The only thing that
changes are absolute bandwidth numbers for a given set of servers. 

Testing other protocols (http, https, netcat, ...) shows full network speed
available between testing servers.

Different IPQoS or Cipher settings do not improve anything.

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