Lets Design, Implement and do Administration of ESX3

Virtualization with VMWare Infrastructure 3.0

Advance concepts

Posted by Preetam on October 27, 2007


The process by which one VM is unscheduled and another scheduled to execute is known as a world switch. This process involves capturing one VM’s processor registers and writing these registers to memory, and reading the registers for the other VM from main memory and, finally, writing these registers to the processor.

Beacon monitoring allows ESX Server to test the links in a bond by sending a packet from one adapter to the other adapters within a virtual switch across the physical links.

AMD PCNet PCI Ethernet adapter (vlance):. This device is used as the default because of its near-universal compatibility – there are DOS drivers for this adapter, as well as Linux, Netware, and all versions of Windows. However the virtual adapter reports link speeds of 10Mbps with only a half-duplex interface,

Vmxnet adapter: If the vlance adapter is not delivering acceptable throughput or if the physical host is suffering from excessive CPU utilization, higher throughput may be possible by changing to the vmxnet adapter, which is a highly-tuned virtual network adapter for VMs.

To handle multiple source MAC addresses, the physical network interface of the ESX server is put into promiscuous mode. This causes its physical MAC address to be masked; all packets transmitted on the network segment are presented to the VMkernel virtual switch interface. Any packets destined for a VM are forwarded to the virtual network adapter through the virtual switch interface. Packets not destined for a VM are immediately discarded.

In virtualization port-based tagging at the physical switch does not provide VLAN isolation between VMs that share the same physical network connection. To address the scenario where broadcast-domain isolation is required between two VMs sharing the same physical network, virtual switches support the creation of port groups that can provide VLAN tagging isolation between VMs within the confines of a virtual switch. Each port group is identified by a network label, which is unique to the current host, and can optionally have a VLAN tagging ID.

When an application within the VM issues a file read or write request to the operating system, the operating system performs a file-to-block conversion and passes the request to the driver. However, the driver in an ESX Server environment does not “talk“ directly to the hardware; instead, the driver passes the block read/write request to the VMkernel where the physical device driver resides and then the read/write request is forwarded to the actual physical hardware device and forwarded to the storage controller.

Unlike Windows and Linux operating systems, ESX Server does not lock a LUN when it is mounted. VMFS is inherently a distributed file system, allowing more than one ESX Server to view the same LUN. This means that, while numerous ESX Server instances may view the contents of a VMFS LUN, only one ESX Server may open a file at any given moment. To an ESX Server and VMFS, when a VM is powered on, the VM disk file is locked.


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