Quantum 6-01376-05 manual StorNext File System Tuning Guide

StorNext File System Tuning

The Distributed LAN (Disk Proxy) Networks

Within each Distributed LAN network, it is best practice to have all SNFS Distributed LAN clients and servers directly attached to the same network switch. A router between a Distributed LAN client and server could be easily overwhelmed by the data rates required.

It is critical to ensure that speed/duplex settings are correct, as this will severely impact performance. Most of the time auto-detectis the correct setting. Some managed switches allow setting speed/duplex, such as 1000Mb/full, which disables auto-detectand requires the host to be set exactly the same. However, performance is severely impacted if the settings do not match between switch and host. For example, if the switch is set to auto-detectbut the host is set to 1000Mb/full, you will observe a high error rate and extremely poor performance. On Linux the mii-diagtool can be very useful to investigate and adjust speed/duplex settings.

In some cases, TCP offload seems to cause problems with Distributed LAN by miscalculating checksums under heavy loads. This is indicated by bad segments indicated in the output of netstat -s. On Linux, the TCP offload state can be queried by running ethtool -k, and modified by running ethtool -K. On Windows it is configured through the Advanced tab of the configuration properties for a network interface.

The internal bus bandwidth of a Distributed LAN client or server can also place a limit on performance. A basic PCI- or PCI-X-based workstation might not have enough bus bandwidth to run multiple Gigabit Ethernet NICs at full speed; PCI Express is recommended but not required.

Similarly, the performance characteristics of NICs can vary widely and ultimately limit the performance of Distributed LAN. For example, some NICs might be able to transmit or receive each packet at Gigabit speeds, but not be able to sustain the maximum needed packet rate. An inexpensive 32-bit NIC plugged into a 64-bit PCI-X slot is incapable of fully utilizing the host's bus bandwidth.

It can be useful to use a tool like netperf to help verify the performance characteristics of each Distributed LAN network. (When using netperf, take care to specify the right IP addresses in order to ensure the network being tested is a Distributed LAN network, not the SNFS dedicated Metadata Network or another network.) For example, if netperf -t TCP_RR reports less than 15,000 transactions per second capacity, a performance penalty might be incurred. Multiple copies of netperf can also be run in parallel to determine the performance characteristics of multiple NICs.

StorNext File System Tuning Guide 19