Why is this network connection so slow?
Solution 1
In my professional experience, I've struggled to get good solid network performance with Samba on GNU/Linux. You mentioned you have achieved speeds of 55 MBps with it, which I believe, so I'm guessing something else is definitely at play.
However, have you tried NFS, FTP and SCP? Are the bandwidth issues consistent across the different protocols? If so, it's likely narrowed down to the physical connection. If you get inconsistent results, then it's likely a software problem.
Aside from testing the other protocols, are you using encryption on the transfer? For example, using rsync -z
is sweet for enabling compression, but it's comes at a CPU cost, which severely impacts overall speed of the transfer. If using SSH
with rsync
, then you have encryption on top of compression, and your CPU will be under a bit of stress, causing severe speed penalties.
Solution 2
Some things you should consider checking:
- Duplex -- if one side thinks the link is full duplex and the other side thinks the link is half duplex, expect badness.
- Defective switch? Bypass it/them.
- Jumbo frames. 9000 byte MTU decreases overhead, which should increase throughput (forfeiting a little latency). It sounds like your problem is so bad that this won't help, though.
- TCP features: ECN, SACK, congestion control alg
- TCP Send/Receive window sizes (details for linux)
netperf is great at troubleshooting network performance. But netcat's not bad in a pinch.
Solution 3
- Try
netstat -i
and look for rx/tx errors. - Try
netstat -s
and look for tcp issues - compare values before and after the file copy and look for large spikes in resets or retransmits.
Paul Keeble
An independent programmer in London working on highly scalable transparent object storage systems.
Updated on September 17, 2022Comments
-
Paul Keeble almost 2 years
I am having some problems with network performance speed on a Linux server running Ubuntu 9.10. Transfer speeds on all types of traffic are around 1.5MB/s on a 1000mbit/s wired ethernet connection. This server has achieved 55MB/s over samba in the recent past. I have not changed the hardware or network set-up. I do run updates on a regular basis and the latest and greatest from Ubuntu's repositories is running on this machine.
Hardware set-up
Desktop Windows PC - 1000 switch - 1000 switch - Linux server
All switches are netgear, and they all show a green light for their connections which means the connection is 1000mbit/s. The lights are yellow when the connection is only 100mbit/s. Other diagnostic information:
root@server:~# ifconfig eth0 Link encap:Ethernet HWaddr 00:0c:6e:3e:ae:36 inet addr:192.168.1.30 Bcast:192.168.1.255 Mask:255.255.255.0 inet6 addr: fe80::20c:6eff:fe3e:ae36/64 Scope:Link UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 RX packets:28678 errors:0 dropped:0 overruns:0 frame:0 TX packets:73531 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:1000 RX bytes:2109780 (2.1 MB) TX bytes:111039729 (111.0 MB) Interrupt:22 lo Link encap:Local Loopback inet addr:127.0.0.1 Mask:255.0.0.0 inet6 addr: ::1/128 Scope:Host UP LOOPBACK RUNNING MTU:16436 Metric:1 RX packets:113 errors:0 dropped:0 overruns:0 frame:0 TX packets:113 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:0 RX bytes:23469 (23.4 KB) TX bytes:23469 (23.4 KB) root@server:~# ethtool eth0 Settings for eth0: Supported ports: [ TP ] Supported link modes: 10baseT/Half 10baseT/Full 100baseT/Half 100baseT/Full 1000baseT/Full Supports auto-negotiation: Yes Advertised link modes: 10baseT/Half 10baseT/Full 100baseT/Half 100baseT/Full 1000baseT/Full Advertised auto-negotiation: Yes Speed: 1000Mb/s Duplex: Full Port: Twisted Pair PHYAD: 0 Transceiver: internal Auto-negotiation: on Supports Wake-on: pg Wake-on: g Current message level: 0x00000037 (55) Link detected: yes root@server:~# mii-tool eth0: negotiated 1000baseT-FD flow-control, link ok
The server thinks its got a 1000mbit/s connection. I have tested the speed of transfer by copying files using Samba. I have also used netcat (nc target 10000 < aBigFile) on the server to transfer to Windows (nc -l -p 10000) and saw similar levels of poor performance.
I tested the speed of the hard drives using hdparm and got:
root@server:~# hdparm -tT /dev/md0 /dev/md0: Timing cached reads: 1436 MB in 2.00 seconds = 718.01 MB/sec Timing buffered disk reads: 444 MB in 3.02 seconds = 147.24 MB/sec
Reading the same file for transfer using DD produced the following:
paul@server:/home/share/Series/New$ dd if=aBigFile of=/dev/null 3200369+1 records in 3200369+1 records out 1638589012 bytes (1.6 GB) copied, 12.7091 s, 129 MB/s
I am stumped. What could be causing the poor network performance which is 2 orders of magnitude lower than what the network is capable of?
-
Paul Keeble almost 14 yearsAt the time of the test these were the only two devices on the network, nothing else was on.
-
Paul Keeble almost 14 yearsAlas there are no TX/RX errors at all after 100MB and the number of resets has been consistently 4 from the beginning to end of test