Logical Domains: architecture and design

Scope: Oracle Solaris 11.4 and, for LDoms, compatible SPARC hardware with Oracle VM Server for SPARC. Examples are educational: verify release, privileges, target names and backups before running changes.

How it works

The four roles

The control domain runs Logical Domains Manager (ldmd) and controls assignments. A service domain offers virtual disk, switch and console services. An I/O domain owns physical I/O resources. A guest domain consumes virtual or assigned resources. A domain can have multiple roles.

A domain is not a Zone

Each LDom has its own Solaris kernel. A non-global Zone shares its global zone kernel; a Kernel Zone provides a separate kernel with different constraints. An LDom can host Zones, so the two technologies can be layered.

Choose the isolation boundary

Use LDoms when separate kernels, independent patch schedules, or resource boundaries are required on supported SPARC systems. Use Zones for lightweight Solaris application separation. Use both for many tenants within an isolated guest.

Service dependencies

A guest using virtual disks or virtual networking depends on the service domains that export those devices. Map these dependencies before maintenance or migration.

Worked examples

Each example explains the question it answers, a reproducible starting point, what to look for, and operational precautions.

1. Inventory domains and roles

Begin every change with an inventory.

ldm list
ldm list -l
ldm list-services
ldm list-dependencies

Interpretation: Look for STATE, FLAGS, CPU, MEMORY, virtual services and dependent guests. Save output before and after a change.

Operational note: Run commands in a test environment first; confirm device names, privileges and release-specific options.

2. Discover the virtualization layer

Find whether Solaris is running as a guest or control domain.

virtinfo -a
uname -a
ldm list

Interpretation: `virtinfo` reports virtualization information where supported; `ldm` administration belongs in the control domain.

Operational note: Run commands in a test environment first; confirm device names, privileges and release-specific options.

3. Record the active configuration

Create an auditable configuration snapshot.

ldm list-constraints -x > /var/tmp/ldoms-before.xml
ldm list-spconfig

Interpretation: XML captures domain constraints; the SP configuration listing shows configurations available for future boots.

Operational note: Run commands in a test environment first; confirm device names, privileges and release-specific options.

Before you finish

Document every virtual disk backend and its owner.
Do not confuse the guest OS boot environment with the hypervisor SP configuration.

Primary documentation

Read the relevant Oracle documentation for exact version-specific flags, supported platforms and limitations: Oracle primary reference ↗.

This field manual is independent, not affiliated with or endorsed by Oracle. Command examples should be adapted to your environment.

Build a guest LDom from scratch →LDoms virtual disks and ZFS backends →LDoms virtual networking, VLANs and resiliency →LDom migration: prerequisites and runbook →