Technical information

Performance Best Practices for VMware vSphere 4.0
14 VMware, Inc.
Hardware Networking Considerations
 Before undertaking any network optimization effort, you should understand the physical aspects of the
network. The following are just a few aspects of the physical layout that merit close consideration:
 Consider using server-class network interface cards (NICs) for the best performance.
 Make sure the NICs are configured to use autonegotiation to set speed and duplex settings, and are
configured for full-duplex mode.
 Make sure the network infrastructure between the source and destination NICs doesn’t introduce
bottlenecks. For example, if both NICs are 1 Gigabit, make sure all cables and switches are capable of
the same speed and that the switches are not configured to a lower speed.
 For the best networking performance, VMware recommends the use of network adapters that support the
following hardware features:
 Checksum offload
 TCP segmentation offload (TSO)
 Ability to handle high-memory DMA (that is, 64-bit DMA addresses)
 Ability to handle multiple Scatter Gather elements per Tx frame
 Jumbo frames (JF)
 On some 10 Gigabit Ethernet hardware network adapters ESX supports NetQueue, a technology that
significantly improves performance of 10 Gigabit Ethernet network adapters in virtualized environments.
 In addition to the PCI and PCI-X bus architectures, we now have the PCI Express (PCIe) architecture.
Ideally single-port 10 Gigabit Ethernet network adapters should use PCIe x8 (or higher) or PCI-X 266 and
dual-port 10 Gigabit Ethernet network adapters should use PCIe x16 (or higher). There should preferably
be no “bridge chip” (e.g., PCI-X to PCIe or PCIe to PCI-X) in the path to the actual Ethernet device
(including any embedded bridge chip on the device itself), as these chips can reduce performance.
 Multiple physical network adapters between a single virtual switch (vSwitch) and the physical network
constitute a NIC team. NIC teams can provide passive failover in the event of hardware failure or network
outage and, in some configurations, can increase performance by distributing the traffic across those
physical network adapters. For more information, see VMware Virtual Networking Concepts, listed in
“Related Publications” on page 8.