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I'm trying to find out why one of my servers, used for fileserving, is sending files at a very slow rate, around 7 Mbits/sec, through nginx.

I've been using iperf3 to test transfer rate between servers, both on Debian 11.

  • FrenchServ : $ iperf3 -s
  • CanadianServ : $ iperf3 -c 195.154.xxx.xxx -P 1 -t 10 -b 1G // Attempts to send, using 1 connection, in 10 sec, 1GB of data

This test over TCP gives the following results :

Connecting to host 195.154.xxx.xxx, port 5201
[  5] local 142.44.xxx.xxx port 60610 connected to 195.154.xxx.xxx port 5201
[ ID] Interval           Transfer     Bitrate         Retr  Cwnd
[  5]   0.00-1.00   sec  1.04 MBytes  8.69 Mbits/sec    0    125 KBytes       
[  5]   1.00-2.00   sec   768 KBytes  6.29 Mbits/sec    0    125 KBytes       
[  5]   2.00-3.00   sec   768 KBytes  6.29 Mbits/sec    0    125 KBytes       
[  5]   3.00-4.00   sec   640 KBytes  5.24 Mbits/sec    0    125 KBytes       
[  5]   4.00-5.00   sec   768 KBytes  6.29 Mbits/sec    0    125 KBytes       
[  5]   5.00-6.00   sec   768 KBytes  6.29 Mbits/sec    0    125 KBytes       
[  5]   6.00-7.00   sec   768 KBytes  6.29 Mbits/sec    0    125 KBytes       
[  5]   7.00-8.00   sec   640 KBytes  5.24 Mbits/sec    0    125 KBytes       
[  5]   8.00-9.00   sec   768 KBytes  6.29 Mbits/sec    0    125 KBytes       
[  5]   9.00-10.00  sec   768 KBytes  6.29 Mbits/sec    0    125 KBytes       
- - - - - - - - - - - - - - - - - - - - - - - - -
[ ID] Interval           Transfer     Bitrate         Retr
[  5]   0.00-10.00  sec  7.54 MBytes  6.32 Mbits/sec    0             sender
[  5]   0.00-10.09  sec  7.08 MBytes  5.89 Mbits/sec                  receiver

iperf Done.

It's very slow, I may stack connections to have faster bandwidth, but would like to keep it 1 connection.

Testing over UDP now.

  • CanadianServ : $ iperf3 -c 195.154.xxx.xxx -P 1 -t 10 -b 1G -u

This outputs:

Connecting to host 195.154.xxx.xxx, port 5201
[  5] local 142.44.xxx.xxx port 37350 connected to 195.154.xxx.xxx port 5201
[ ID] Interval           Transfer     Bitrate         Total Datagrams
[  5]   0.00-1.00   sec   113 MBytes   950 Mbits/sec  81331  
[  5]   1.00-2.00   sec   114 MBytes   955 Mbits/sec  81773  
[  5]   2.00-3.00   sec   114 MBytes   956 Mbits/sec  81887  
[  5]   3.00-4.00   sec   114 MBytes   957 Mbits/sec  81904  
[  5]   4.00-5.00   sec   114 MBytes   956 Mbits/sec  81862  
[  5]   5.00-6.00   sec   114 MBytes   957 Mbits/sec  81913  
[  5]   6.00-7.00   sec   114 MBytes   957 Mbits/sec  81909  
[  5]   7.00-8.00   sec   114 MBytes   957 Mbits/sec  81915  
[  5]   8.00-9.00   sec   114 MBytes   956 Mbits/sec  81880  
[  5]   9.00-10.00  sec   114 MBytes   957 Mbits/sec  81904  
- - - - - - - - - - - - - - - - - - - - - - - - -
[ ID] Interval           Transfer     Bitrate         Jitter    Lost/Total Datagrams
[  5]   0.00-10.00  sec  1.11 GBytes   956 Mbits/sec  0.000 ms  0/818278 (0%)  sender
[  5]   0.00-10.41  sec   600 MBytes   484 Mbits/sec  0.029 ms  387089/818278 (47%)  receiver

iperf Done.

UDP actual bandwidth tops around 500 Mbits/sec, which is perfectly fine given both server's network interfaces.

How can I make TCP transfer use more bandwidth ?? I've tried on my local computer, I get around 30 Mbits/sec on TCP transfers.

Pardhu Katreddy
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Baptiste Placé
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1 Answers1

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Found the solution in the server configuration, TCP Window was disabled as recommended for standard Apache configuration (described here)

$ vi /etc/sysctl.conf

# Set this value and save
net.ipv4.tcp_window_scaling = 1

# check with
$ sysctl -p

Now we need to adjust the TCP Window value, as explained here or here.

Baptiste Placé
  • 101
  • 3