Introduction to LDOM's

Logical domains are discrete instances of the Solaris OE running independently within a virtualized environment. Each logical domain has its own virtual cpu, memory, OBP, console, networking, storage, and I/O components. These components are configured with a combination of different technologies.

• sun4v Platform Hypervisor
• Logical Domain Management Software
• Solaris OE

The hypervisor provides the mechanism for masking and virtualizing the resources on the platform. The hypervisor is a light-weight software layer built into the ALOM CMT firmware. The hypervisor also helps to abstract the low-level hardware details from logical domains.

The logical domain management software is the nexus for control and configuration of the hypervisor. This software provides a CLI to controlling and configuring the resources that define each logical domain. Only one logical domain can run the management software. This logical domain is known as the "primary" or control domain. More about the different LDOM types in a moment.

The Solaris OE provides support for the sun4v platform, dynamic reconfiguration, and virtual devices. At this time, you need Solaris 10 Update 3 (11/06) or Nevada build 57. It's not possible to use Solaris 9 or below for LDOM's, as the platform support is not there.

There are four types of LDOM's that can be created:

• Control Domain
• Service Domain
• I/O Domain
• Guest Domain

The control domain is the first installed LDOM or instance of Solaris on the platform. This LDOM contains the Logical Domain Management (SUNWldm) software for managing the platform. It is from this LDOM that all of the hardware platform specifics are visible and configurable. The control and configuration of the platform is communicated through LDC's (Logical Domain Channels). It is through this mechanism that the configuration, virtual devices, and virtual services communications are relayed.

A service domain is an LDOM that has control over either one or more PCI-E controllers. It consists of an instance of the Solaris OE. No additional software is required, the control domain will configure the virtualized devices and service within a service domain. The service domain will then service the I/O for these virtualized components for guest domains to utilize. The service domain has direct control over the hardware under its PCI-E controller. There are only two in the Sun Fire T2000. So only two service domains are configurable, one of which must also be the control domain. It is important to remember that the control domain is one of the service domains. If a second service domain is created, this is called a Split PCI-E configuration. More about that later.

An I/O domain is exactly like a service domain, except for the fact that none of its devices or services are virtualized for guest domains. This is useful if you have an application that requires direct access to a PCI-E device for performance or some other reason.

A guest domain is a consumer of virtualized devices and services. Meaning that it does not virtualize any devices or services for other domains. It is independent of other guest domains. However, it is dependent upon the service domains that provide its virtual devices and services. A guest domain consist of its own instance of Solaris OE. This is where your applications will typically live as consuming resources in the control or services domains affects the platform as a whole.

While a fully configured Sun Fire T2000 has a total of 32 CPU threads, it's probably not a good idea to create 32 LDOM's. As this would under power the control and services domains.

The next post will be about the installation of the firmware, patches, and Logical Domain Management software.

Disclaimer: This post only covers the Early Access RC3 of the LDOM technology, which is in pre-release.