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Troubleshooting slow network file transfer

2021-06-25

We have a Hadoop data cluster. Recently, my colleague noticed that data transfer between servers was slow. Not all are slow; only half of them have problems.

The first tool that comes to mind is iperf3. After installing, I run iperf3 -s then iperf3 -c. While other servers have bandwidth > 900 Mbits/sec, the slow ones are just:

[ ID] Interval           Transfer     Bandwidth       Retr  Cwnd
[  4]   0.00-1.00   sec  11.9 MBytes  99.4 Mbits/sec    0    170 KBytes
[  4]   1.00-2.00   sec  11.1 MBytes  93.3 Mbits/sec    0    204 KBytes
[  4]   2.00-3.00   sec  10.9 MBytes  91.7 Mbits/sec    0    204 KBytes
[  4]   3.00-4.00   sec  8.26 MBytes  69.3 Mbits/sec  102    154 KBytes
[  4]   4.00-5.00   sec  10.9 MBytes  91.8 Mbits/sec    3    157 KBytes
[  4]   5.00-6.00   sec  10.9 MBytes  91.7 Mbits/sec    0    165 KBytes
[  4]   6.00-7.00   sec  10.9 MBytes  91.7 Mbits/sec    0    168 KBytes
[  4]   7.00-8.00   sec  10.9 MBytes  91.7 Mbits/sec    0    173 KBytes
[  4]   8.00-9.00   sec  10.9 MBytes  91.7 Mbits/sec    0    173 KBytes
[  4]   9.00-10.00  sec  10.9 MBytes  91.7 Mbits/sec    0    173 KBytes
- - - - - - - - - - - - - - - - - - - - - - - - -
[ ID] Interval           Transfer     Bandwidth       Retr
[  4]   0.00-10.00  sec   108 MBytes  90.4 Mbits/sec  105             sender
[  4]   0.00-10.00  sec   107 MBytes  89.5 Mbits/sec                  receiver