I have recently update from FC3 to FC6. I was running a gigabit card under FC3 with no issues. Under FC6, when I transfer large amounts of data from my NFS-mounted NAS box (also w a GbE card), the gigabit network connection dies completely and I have no connectivity. I suspect this has something to do with exceeding buffers or transmission window sizes or something to that effect.

To be sure that I don't have other issues, I have recompiled the kernel, and I have tried two different gigabit cards. I see no errors in /var/log/messages or dmesg or dropped packets in ifconfig.

I'm running on a Athlon XP 2800 processor that is running a relatively slow bus (33MHz). That is why I suspect that the network bandwidth is exceeding the I/O performance of my box. Is that what is likely to be causing my problems? What can I check to verify? What parameter changes should I make to fix this issue? I have tried the following:

# increase TCP max buffer size
net.core.rmem_max = 16777216
net.core.wmem_max = 16777216
# increase Linux autotuning TCP buffer limits
# min, default, and max number of bytes to use
net.ipv4.tcp_rmem = 4096 87380 16777216
net.ipv4.tcp_wmem = 4096 65536 16777216
# don't cache ssthresh from previous connection
net.ipv4.tcp_no_metrics_save = 1
# recommended to increase this for 1000 BT or higher
net.core.netdev_max_backlog = 2500
net.ipv4.tcp_timestamps = 1
net.ipv4.tcp_window_scaling = 1
net.ipv4.tcp_sack = 0
Reply With Quote