6.7

Chart Analysis
Network performance depends on the application workload and network configuration. Dropped network
packets indicate a bottleneck in the network. To determine whether packets are being dropped, use
esxtop or the advanced performance charts to examine the droppedTx and droppedRx network counter
values.
If packets are being dropped, adjust the virtual machine shares. If packets are not being dropped, check
the size of the network packets and the data receive and transfer rates. In general, the larger the network
packets, the faster the network speed. When the packet size is large, fewer packets are transferred,
which reduces the amount of CPU required to process the data. When network packets are small, more
packets are transferred but the network speed is slower because more CPU is required to process the
data.
Note In some instances, large packets might result in a high network latency. To check the network
latency, use the VMware AppSpeed performance monitoring application or a third-party application.
If packets are not being dropped and the data receive rate is slow, the host is probably lacking the CPU
resources required to handle the load. Check the number of virtual machines assigned to each physical
NIC. If necessary, perform load balancing by moving virtual machines to different vSwitches or by adding
more NICs to the host. You can also move virtual machines to another host or increase the host CPU or
virtual machine CPU.
If you experience network-related performance problems, also consider taking the following actions.
Table 1‑74. Networking Performance Enhancement Advice
# Resolution
1 Verify that VMware Tools is installed on each virtual machine.
2 If possible, use vmxnet3 NIC drivers, which are available with VMware Tools. They are optimized for high performance.
3 If virtual machines running on the same host communicate with each other, connect them to the same vSwitch to avoid
transferring packets over the physical network.
4 Assign each physical NIC to a port group and a vSwitch.
5 Use separate physical NICs to handle the different traffic streams, such as network packets generated by virtual machines,
iSCSI protocols, vMotion tasks.
6 Ensure that the physical NIC capacity is large enough to handle the network traffic on that vSwitch. If the capacity is not
enough, consider using a high-bandwidth physical NIC (10 Gbps). Alternatively, consider moving some virtual machines to a
vSwitch with a lighter load or to a new vSwitch.
7 If packets are being dropped at the vSwitch port, increase the virtual network driver ring buffers where applicable.
8 Verify that the reported speed and duplex settings for the physical NIC match the hardware expectations and that the
hardware is configured to run at its maximum capability. For example, verify that NICs with 1 Gbps are not reset to 100 Mbps
because they are connected to an older switch.
9 Verify that all NICs are running in full duplex mode. Hardware connectivity problems might result in a NIC resetting itself to a
lower speed or half duplex mode.
10 Use vNICs that are TCP Segmentation Offload (TSO)-capable, and verify that TSO-Jumbo Frames are enabled where
possible.
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