Logical Domain Roles
All logical domains are the same except for the roles that you specify for them. There are multiple roles that logical domains can perform such as:
- Control domain
- Service domain
- I/O domain
- Guest domain
The Control domain, as its name implies, controls the logical domain environment. It is used to configure machine resources and guest domains, and provides services necessary for domain operation, such as virtual console service. The control domain also normally acts as a service domain.
Service domains present virtual services, such as virtual disk drives and network switches, to other domains. In most cases, guest domains perform I/O via bridged access through services domains, which are usually I/O domains and directly connected to the physical devices. Service domains can provide virtual LANs and SANs as well as bridge through to physical devices. Disk images can reside on complete local physical disks, shared SAN block devices, their slices, or even on files contained on a local UFS or ZFS file system, or on a shared NFS export.
I/O domains have direct ownership of a PCI bus and direct access to physical I/O devices, such as a network card in a PCI controller. It shares the devices to other domains in the form of virtual devices. You can have a maximum of two I/O domains for the UltraSPARC T1 (Niagara) servers, one of which also must be the control domain. UltraSPARC T2 Plus, SPARC T3, and SPARC T4 servers can have as many as 4 I/O domains. Multiple I/O domains can be configured to provide resiliency against failures.
Guest domains run an operating system instance without performing any of the above roles, but leverage the services provided by the above in order to run applications.
Control and service functions can be combined within domains, however it is recommended that user applications not run within control or service domains in order to protect domain stability and performance.
Read more about this topic: Logical Domains
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