Control domain. The Logical Domains Manager runs in this domain, which enables you to create and manage other logical domains, and to allocate virtual resources to other domains. You can have only one control domain per server. The control domain is the first domain created when you install the Logical Domains software. The control domain is named primary.
Service domain. A service domain provides virtual device services to other domains, such as a virtual switch, a virtual console concentrator, and a virtual disk server. Any domain can be configured as a service domain.
I/O domain. An I/O domain has direct ownership of and direct access to physical I/O devices, such as a network card in a PCI EXPRESS® controller. An I/O domain is often used as a service domain to share physical devices with other domains in the form of virtual devices. The control domain is an I/O domain, and it can also be used as a service domain. The number of I/O domains that you can have depends on your platform. For example, if you are using a Sun SPARC Enterprise® Server T5440, you can have up to four I/O domains.
Guest domain. A guest domain is a non-I/O domain that consumes virtual device services that are provided by one or more service domains. A guest domain does not have any physical I/O devices, but only has virtual I/O devices, such as virtual disks and virtual network interfaces.
You can install the Logical Domains Manager on an existing system that is not already configured with Logical Domains. In this case, the current instance of the OS becomes the control domain. Also, the system is configured as a Logical Domains system that has only one domain, the control domain. After configuring the control domain, you can balance the load of applications across other domains to make the most efficient use of the entire system. You do this by adding domains and moving those applications from the control domain to the new domains.