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Hey,
lately I tried syncing files between my desktop pc (running Arch Linux) und my laptop (running OpenSuse 12.3) connected on a gigabit network.
Rsync was incredibly slow, so I tried measuring network performance using iperf and noticed a significantly lower speed when copying from OpenSuse to Arch, rather than the other way around.
# Laptop -> Desktop (OpenSuse -> Arch)
[user@Desktop ~ ]$ iperf -s
------------------------------------------------------------
Server listening on TCP port 5001
TCP window size: 85.3 KByte (default)
------------------------------------------------------------
[ 4] local 192.168.1.55 port 5001 connected with 192.168.1.77 port 45103
[ ID] Interval Transfer Bandwidth
[ 4] 0.0-10.0 sec 79.9 MBytes 66.9 Mbits/secuser@Laptop:~$ iperf -c 192.168.1.55
------------------------------------------------------------
Client connecting to 192.168.1.55, TCP port 5001
TCP window size: 22.9 KByte (default)
------------------------------------------------------------
[ 3] local 192.168.1.77 port 45103 connected with 192.168.1.55 port 5001
[ ID] Interval Transfer Bandwidth
[ 3] 0.0-10.0 sec 79.9 MBytes 67.0 Mbits/sec
# Desktop -> Laptop (Arch -> OpenSuse)
[user@Desktop ~ ]$ iperf -c 192.168.1.77
------------------------------------------------------------
Client connecting to 192.168.1.77, TCP port 5001
TCP window size: 85.0 KByte (default)
------------------------------------------------------------
[ 3] local 192.168.1.55 port 45037 connected with 192.168.1.77 port 5001
[ ID] Interval Transfer Bandwidth
[ 3] 0.0-10.0 sec 1003 MBytes 841 Mbits/sec
user@Laptop:~$ iperf -s
------------------------------------------------------------
Server listening on TCP port 5001
TCP window size: 85.3 KByte (default)
------------------------------------------------------------
[ 4] local 192.168.1.77 port 5001 connected with 192.168.1.55 port 45037
[ ID] Interval Transfer Bandwidth
[ 4] 0.0-10.0 sec 1003 MBytes 840 Mbits/sec
My first idea was that possibly the network switch between them may be responsible,
so I connected the two machines directly, but that doesn't change the observed behaviour.
Any ideas how that can be possible? (840 vs 67 Mbit/s) is a tremendous difference, obviously.
Althrough I'm not even sure which machine is configured incorrectly.
Last edited by TcShadowWalker (2014-05-11 16:20:19)
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After fiddling around with the cabling and different configurations, I can confirm the problem actually lies with OpenSuse.
If I use iperf from a Live CD (grml) on the Laptop, both directions give full performance.
On the other hand, if I boot grml on the Desktop (replacing Arch) and the Laptop continues running OpenSuse, the problem remains.
What is even weirder is the fact that OpenSuse also manages to give full performance, if I have the cables connected before booting the system.
As soon as the system is running and I disconnect the connection for any time, the problem occurs again.
I suspect some form of duplex mismatch (http://en.wikipedia.org/wiki/Duplex_mismatch).
However, using ethtool, both systems agree that Auto-negotiation is on, the connection is full duplex and the speed should be 1000Mb/s (1000baseT/Full).
I guess I will simply ditch OpenSuse and install another Linux distribution on the Laptop.
Although I would like to understand the actual cause of the problem.
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