By default, the network buffer size is set to 1 MB for TCP, and 2 MB for UDP. The TCP buffer size can set a limit on file transfers, which can negatively affect performance for Direct NFS Client users.

To check the current TCP buffer size, enter the following command:

# sysctl -a |grep -e net.ipv4.tcp_[rw]mem

The output of this command is similar to the following:

net.ipv4.tcp_rmem = 4096        87380   1056768
net.ipv4.tcp_wmem = 4096        16384   1056768

Oracle recommends that you set the value based on the link speed of your servers. For example, perform the following steps:

1. As root, use a text editor to open /etc/sysctl.conf, and add or change the following:

   net.ipv4.tcp_rmem = 4096        87380   4194304
   net.ipv4.tcp_wmem = 4096        16384   4194304
   

2. Apply your changes by running the following command:

   # sysctl -p
   

3. Restart the network:

   # /etc/rc.d/init.d/network restart