The Network (Mbps) chart displays network speed for the 10 hosts in the cluster with the most network usage.

This chart is located in the Hosts view of the Cluster Performance tab.

Table 1. Data Counters

Chart Label

Description

<host>

Average rate at which data is transmitted and received across all NIC instances on the host.

  • Counter: usage

  • Stats Type: Rate

  • Unit: Megabits per second (Mbps)

  • Rollup Type: Average (Minimum/Maximum)

  • Collection Level: 1 (4)

Chart Analysis

Network performance depends on 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 high network latency. To check 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 virtual switches 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 actions listed below.

Table 2. 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 virtual switch to avoid transferring packets over the physical network.

4

Assign each physical NIC to a port group and a virtual switch.

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 virtual switch. If the capacity is not enough, consider using a high-bandwidth physical NIC (10Gbps) or moving some virtual machines to a virtual switch with a lighter load or to a new virtual switch.

7

If packets are being dropped at the virtual switch 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 1Gbps are not reset to 100Mbps 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 VM network adapters that are TSO-capable, and verify that TSO-Jumbo Frames are enabled where possible.