Quantum 6-01376-07 manual Network Configuration and Topology

Network Configuration and Topology

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The Distributed LAN (Disk Proxy) Networks

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 ethtool command 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, on a system with multiple NICs, take care to specify the right IP addresses in order to ensure the network being tested is the one you will be running Distributed LAN over. 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.

For maximum throughput, SNFS distributed LAN can utilize multiple NICs on both clients and servers. In order to take advantage of this feature, each of the NICs on a given host must be on a different IP subnetwork. (This is a requirement of TCP/IP routing, not of SNFS - TCP/IP can't utilize multiple NICs on the same subnetwork.) An example of this is shown in the following illustration.

StorNext File System Tuning Guide 19