In an Oracle VM Server for SPARC environment, you can provision up to 128 domains on a system (up to 256 on a Fujitsu M10 server). Some servers, particularly single-processor and some dual-processor systems, have a limited number of I/O buses and physical I/O slots. As a result, you might be unable to provide exclusive access to a physical disk and network devices to all domains on these systems. You can assign a PCIe bus or endpoint device 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. This limitation on the number of physical I/O devices that can be directly accessed is addressed by implementing a virtualized I/O model. See Chapter 5, Configuring I/O Domains.
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.
Oracle VM Server for SPARC 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:
Virtual disk client (vdc), which exports a block device interface
Virtual disk service (vds), which processes disk requests on behalf of the virtual disk client and submits them to the back-end storage that resides on the service domain
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 an Oracle VM Server for SPARC 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 console traffic for all domains, and interfaces with the virtual network terminal server daemon (vntsd) to provide access to each console through a UNIX socket.