System information

Raw Device Mapping
A raw device mapping (RDM) is a special file in a VMFS volume that acts as a proxy for a raw device, such as
a SAN LUN. With the RDM, the SAN LUN can be directly and entirely allocated to a virtual machine. The
RDM provides some of the advantages of a virtual disk in the VMFS file system, while keeping some
advantages of direct access to physical devices.
An RDM might be required if you use Microsoft Cluster Service (MSCS) or if you run SAN snapshot or other
layered applications on the virtual machine. RDMs enable systems to use the hardware features inherent to
SAN arrays. However, virtual machines with RDMs do not display performance gains compared to virtual
machines with virtual disk files stored on a VMFS datastore.
For more information on the RDM, see the ESX Configuration Guide or ESXi Configuration Guide.
Interacting with ESX/ESXi Systems
You can interact with ESX/ESXi systems in several different ways. You can use a client or, in special cases,
interact programmatically.
Administrators can interact with ESX/ESXi systems in one of the following ways:
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With a GUI client (vSphere Client or vSphere Web Access). You can connect clients directly to the ESX/
ESXi host, or you can manage multiple ESX/ESXi hosts simultaneously with vCenter Server.
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Through the command-line interface. vSphere Command-Line Interface (vSphere CLI) commands are
scripts that run on top of the vSphere SDK for Perl. The vSphere CLI package includes commands for
storage, network, virtual machine, and user management and allows you to perform most management
operations. For more information, see vSphere Command-Line Interface Installation and Reference Guide.
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ESX administrators can also use the ESX service console, which supports a full Linux environment and
includes all vSphere CLI commands. Using the service console is less secure than remotely running the
vSphere CLI. The service console is not supported on ESXi.
VMware vCenter Server
vCenter Server is a central administrator for ESX/ESXi hosts. You can access vCenter Server through a vSphere
Client or vSphere Web Access.
vCenter Server
vCenter Server acts as a central administrator for your hosts connected on a
network. The server directs actions upon the virtual machines and VMware
ESX/ESXi.
vSphere Client
The vSphere Client runs on Microsoft Windows. In a multihost environment,
administrators use the vSphere Client to make requests to vCenter Server,
which in turn affects its virtual machines and hosts. In a single-server
environment, the vSphere Client connects directly to an ESX/ESXi host.
vSphere Web Access
vSphere Web Access allows you to connect to vCenter Server by using an
HTML browser.
Chapter 1 Overview of VMware ESX/ESXi
VMware, Inc. 13