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I have two virtual servers under VMware Server 2, both running CentOS Linux. Server A is under fairly constant load of about 4, server B is under load anywhere between 1 and 4. Both are on the host and thus connected to the same network, same router, etc. I am noting that the network perfoamce on server B is atrocious compared to that of A. I created a 10 MB file on both servers and when transferring the file via FTP, SFTP or HTTP, I get over double the transfer speed when coping from A to my workstation than from B to my workstation.

I assume something in sysctl or /proc/sys/net is misconfigured on server B but am unsure of where to look...

EDIT: I compared everything in /proc/sys/net on both machines, they're almost identical. I also noticed that download times are much worse on server B. Any advice to troubleshoot possible network problems would be greatly appreciated!

EDIT2: Here are some results from iperf for server A:

[ ID] Interval       Transfer     Bandwidth
[  4]  0.0-11.2 sec    632 KBytes    463 Kbits/sec
[ ID] Interval       Transfer     Bandwidth
[  4]  0.0-10.7 sec    624 KBytes    477 Kbits/sec
[ ID] Interval       Transfer     Bandwidth
[  4]  0.0-20.2 sec  1.16 MBytes    483 Kbits/sec
[ ID] Interval       Transfer     Bandwidth
[  4]  0.0-22.2 sec  1.23 MBytes    463 Kbits/sec
[ ID] Interval       Transfer     Bandwidth
[  4]  0.0-61.1 sec  3.35 MBytes    460 Kbits/sec
[ ID] Interval       Transfer     Bandwidth
[  3]  0.0-10.1 sec    688 KBytes    560 Kbits/sec

And from server B:

[ ID] Interval       Transfer     Bandwidth
[  5]  0.0- 9.7 sec    400 KBytes    339 Kbits/sec
[ ID] Interval       Transfer     Bandwidth
[  4]  0.0- 8.0 sec    400 KBytes    409 Kbits/sec
[ ID] Interval       Transfer     Bandwidth
[  4]  0.0- 9.9 sec    408 KBytes    338 Kbits/sec
[ ID] Interval       Transfer     Bandwidth
[  4]  0.0-20.3 sec    776 KBytes    313 Kbits/sec
[ ID] Interval       Transfer     Bandwidth
[  4]  0.0-18.7 sec    744 KBytes    325 Kbits/sec
[ ID] Interval       Transfer     Bandwidth
[  4]  0.0-53.0 sec   2.16 MBytes    343 Kbits/sec

So, there's a difference there, and I'm not sure why. But it's not nearly as large as a difference as I see when using FTP/SFTP/HTTP. Any tips on troubleshooting further would be greatly appreciated...

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2 Answers

up vote 1 down vote accepted

It turned out to be that a number of the ext3 partitions on server B had errors. Server B eventually kernel paniced (I believe due to bad RAM) and upon reboot, fsck corrected a number of problems. Since that time, the issue has gone away. This leads me to believe that the filesystem errors somehow caused the behavior I was seeing...

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try to run a tcpdump, see why you're getting bad network performance. does the virtual NIC in both servers use PV?

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I've used tcpdump before to watch traffic over the wire, but how would I use it to troubleshoot performance? Also, forgive my ignorance, but what is PV? –  Josh Oct 9 '09 at 15:27
    
to troubleshoot performance you can see whether there are dropped packets and excess repeating during transmission. PV stands for paravirtualized, i.e. not completely software driven NICs –  dyasny Oct 10 '09 at 14:24
    
@dyasny: thanks. I'm not seeing much packet loss, both servers loov very similar. Neither one is paravirtualized. –  Josh Oct 12 '09 at 12:46
    
Is the physical NIC on the host by any chance Broadcom? –  dyasny Oct 13 '09 at 10:51
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