What is Oracle VM for SPARC / LDOM?

Oracle VM for SPARC (LDOMs) is a hardware virtualization technology built into SPARC servers. A single physical SPARC system can be split into multiple domains, each behaving like an independent server: its own OS instance, hostname, IPs, applications and security boundaries.

Hardware virtualisation

LDOMs use the SPARC hypervisor in firmware to carve up CPU, memory and I/O into separate domains.

Multiple domains

Each domain can run its own Solaris (or other supported OS) with separate lifecycle and resources.

Isolation & flexibility

Faults in one domain do not crash others. Resources can be reallocated dynamically in many cases.

Why use LDOMs?

Consolidate many workloads on one SPARC server.
Separate environments: prod / UAT / dev / DR on same box.
Assign dedicated resources per application or tenant.
Support different OS versions / patch levels in separate domains.

Hypervisor basics – Type 1 vs Type 2 and where LDOMs fits

A hypervisor is the layer that creates and manages virtual machines or domains.

Type 1 (bare metal) hypervisor

Runs directly on hardware (no host OS underneath).
Examples: Oracle VM for SPARC (LDOMs), VMware ESXi, Hyper-V (bare metal mode).
High performance and isolation.

Type 2 (hosted) hypervisor

Runs on top of an OS as an application.
Examples: VirtualBox, VMware Workstation.
Simpler for desktops/labs; not as close to hardware.

Where does LDOM hypervisor sit?

SPARC servers implement the hypervisor in firmware – a type 1 bare metal hypervisor.
Solaris itself runs inside a domain (often the primary domain), not directly on hardware.
Domains talk to the hypervisor for CPU, memory and I/O access.

How LDOMs differ from other virtualization solutions

Compared to zones

Zones share a single OS instance (same kernel).
LDOMs are separate domains at hardware level.
You can run zones inside a domain – two-level virtualization.

Compared to x86 hypervisors

LDOMs are tightly integrated with SPARC CPU features.
I/O virtualization often uses service and I/O domains.
Management is via ldm CLI (and sometimes OEM tools).

Key LDOM terms: primary, control, service, I/O and guest domains

Primary domain

First domain created on the system, usually at factory.
Typically runs Solaris and LDoms Manager (ldmd).
Often combined with other roles: control + service + I/O.

Control domain

Domain that runs ldmd and controls configuration of all LDOMs.
You run ldm commands here (create, bind, start, stop domains).
Usually the same as the primary domain.

Service domain

Provides virtual services to other domains:
– Virtual disk service (VDS) for vdisks.
– Virtual network switch (vsw) for vnets.
Can be the same as control/primary domain.

I/O domain (root domain)

Domain with direct ownership of physical PCIe root complex or HBAs.
Direct access to physical disks/NICs; can export them as virtual devices.
You can have multiple I/O domains for high availability.

Guest domain (logical domain)

Regular domain that runs workloads (DB, apps, web, etc.).
Receives virtual CPUs, memory and I/O from the hypervisor and service/I/O domains.
Does not control other domains.

Summary: big picture of LDOMs

SPARC hypervisor (type 1) splits hardware into domains.
Control/primary domain runs ldmd, manages other domains via ldm.
Service/I/O domains provide virtual disks and networks.
Guest domains run applications using virtual resources.