In a Logical Domains environment, you can provision up to 128 domains on an UltraSPARC® T2 Plus processor system. These systems have a limited number of I/O buses and physical I/O slots. As a result, you cannot provide exclusive access to a physical disk and network devices to all domains on these systems. You can assign a PCI bus to a domain to provide it with access to a physical device. Note that this solution is insufficient to provide all domains with exclusive device access. See I/O Domains and PCI EXPRESS Buses. This lack of direct physical I/O device access is addressed by implementing a virtualized I/O model.
Any logical domains that have no physical I/O access are configured with virtual I/O devices that communicate with a service domain. The service domain runs a virtual device service to provide access to a physical device or to its functions. In this client-server model, virtual I/O devices either communicate with each other or with a service counterpart through interdomain communication channels called logical domain channels (LDCs). The virtualized I/O functionality includes support for virtual networking, storage, and consoles.
Logical Domains uses the virtual network device and virtual network switch device to implement virtual networking. The virtual network (vnet) device emulates an Ethernet device and communicates with other vnet devices in the system by using a point-to-point channel. The virtual switch (vsw) device primarily functions as a multiplexor of all the virtual network's incoming and outgoing packets. The vsw device interfaces directly with a physical network adapter on a service domain, and sends and receives packets on behalf of a virtual network. The vsw device also functions as a simple layer-2 switch and switches packets between the vnet devices connected to it within the system.
The virtual storage infrastructure uses a client-server model to enable logical domains to access block-level storage that is not directly assigned to them. The model uses the following components:
Although the virtual disks appear as regular disks on the client domain, most disk operations are forwarded to the virtual disk service and processed on the service domain.
In a Logical Domains environment, console I/O from the primary domain is directed to the service processor. The console I/O from all other domains is redirected to the service domain that is running the virtual console concentrator (vcc). The domain that runs the vcc is typically the primary domain. The virtual console concentrator service functions as a concentrator for all domains' console traffic, and interfaces with the virtual network terminal server daemon (vntsd) to provide access to each console through a UNIX socket.