3.5.1 Matrix Server Administration Guide

Chapter 8: Configure MxFS-Linux 169

Kernel

In the kernel, certain tunable parameters affect allocations for buffers and

the TCP core. TCP window scaling, which is enabled by default, allows

the receiving system to scale the local TCP receive window larger than

the default 64 KB. This occurs only if the system settings for the default

and maximum TCP socket buffer sizes are set to allow larger than

“normal” buffers. The recommended parameter changes, described later

in this document, were developed with this consideration in mind and

provide better NFS performance than the default values.

See “Tuning Parameters” on page 170 for descriptions of the parameters

and their recommended values. In general, we recommend that you

increase the values for several parameters that affect TCP buffers. We also

recommend that certain tunable parameters be disabled, either because of

a known kernel issue or because they do not enhance NFS performance.

Network

The following changes can improve NFS performance:

•Use Gigabit Ethernet.

• Disable Ethernet flow control. The TCP/IP protocol has its own flow-

control mechanism and can better handle overrun conditions. (Check

your NIC documentation to determine whether this feature can be

disabled.)

Other Network Tuning Considerations

The following network changes should be made only if you have

adjusted the tuning parameters and made the NIC changes described

above and suspect that your systems still have networking issues.

• TCP Segmentation Offload (TSO). The TCP protocol stack in the

kernel must take a stream of data and convert it into IP datagrams for

transmission over the network. The TSO feature offloads this action to

the hardware in the NIC. Testing has shown that disabling this feature

can improve network performance. (Check the documentation for

your NIC to determine whether changing the value is supported.)

• Depending on your network interface card, you may want to increase

the size of the NIC transmit queue maintained by the driver for the