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VMware VMDirectPath I/O

August 3, 2009
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by Simon Long

What is VMware VMDirectPath I/O?

VMDirectPath allows guest operating systems to directly access an I/O device, bypassing the virtualization layer. This direct path, or passthrough can improve performance for VMware ESX systems that utilize high-speed I/O devices, such as 10 Gigabit Ethernet. A single VM can connect to up to two passthrough devices.

VMDirectPath I/O is experimentally supported for the following Storage and Network I/O devices:

  • QLogic QLA25xx 8 Gb Fibre Channel adapters
  • Emulex LPe12000 8 Gb Fibre Channel adapters
  • LSI 3442e-R and 3801e (1068 chip based) 3 Gb SAS adapters
  • Intel 82598 10 Gigabit Ethernet controller
  • Broadcom 57710 and 57711 10 Gigabit Ethernet controllers

VMware regularly adds support for new hardware. Check your hardware’s support at the VMware Hardware Compatibility Guide portal.

What are the advantages of using VMware VMDirectPath I/O?

VMDirectPath I/O can be used when your guest OS needs a greater performance from the I/O device. It also allows the use of I/O devices, which are not supported by the ESX server directly, to be linked to VM’s as the virtualization layer is bypassed.

What are the disadvantages of using VMware VMDirectPath I/O?

There are a couple of disadvantages in using VMDirectPath I/O on a VM. They are:

  • Once you have your VM directly connected to an I/O device, your VM will no longer be able to use features such as VMotion and DRS.
  • You cannot have two devices in two different contexts (for example, one used by VMkernel and one in pass-through) using the same PCI slot. For example, the dual head NIC is dedicated to the VMkernel OR is available for pass-through. If you select one, the other is automatically selected as well. A dialog informs you why this occurred.

How is VMware VMDirectPath I/O configured on an ESX Host?

To configure VMDirectPath I/O on your ESX Host, follow the steps on the VMware guide: Configuring VMDirectPath I/O pass-through devices on an ESX host

Resources:

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VMware VMDirectPath I/O

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