HCI vs UCI: Deployment Models

Two Ways to Deploy VergeOS

VergeOS is unique among infrastructure platforms because it supports two distinct deployment models from the same software installation:

• HCI (Hyperconverged Infrastructure) — Compute and storage run on every node. Resources scale together.
• UCI (Ultra Converged Infrastructure) — Compute and storage run on dedicated, separate node types. Resources scale independently.

Most competing platforms (VMware vSAN, Nutanix) only support HCI. VergeOS gives you both options — and you can even combine them within a single system.

HCI: Hyperconverged Infrastructure

In an HCI deployment, every node in the cluster contributes both storage capacity and compute resources. When you need more of either, you add another node — which adds both.

How It Works

The simplest VergeOS deployment is a 2-node HCI cluster. Two controller nodes form a single cluster that handles storage (vSAN) and compute (VM workloads). Both nodes contribute tier-0 and tier-1 disks to the shared storage pool, and both nodes run virtual machines.

To grow, you add scale-out nodes to the same cluster. Each scale-out node joins via network auto-detection and immediately contributes additional storage and compute capacity.

When to Choose HCI

Scenario	Why HCI Works
Small deployments (2—8 nodes)	Minimal complexity, every node pulls double duty
Balanced workloads	When storage and compute demands grow at roughly the same rate
Edge / remote sites	2-node clusters with full HA and a small physical footprint
Evaluation and testing	Fastest path to a working VergeOS system
Budget-conscious	Fewer total nodes needed for small-to-medium workloads

Key Characteristics

• Minimum: 2 nodes (controller pair)
• Scaling: Add scale-out nodes to the same cluster (up to 200+ nodes)
• Node roles: All nodes run storage and compute
• Cluster count: 1
• Simplicity: Easiest to deploy and manage

UCI: Ultra Converged Infrastructure

UCI separates storage and compute onto dedicated node types, each in its own cluster. This lets you scale each resource tier independently — add storage nodes when you need more capacity, or compute nodes when you need more CPU and RAM, without buying both.

How It Works

A UCI deployment starts with the same 2-node controller pair, but the controllers manage the system without running production workloads or storing user data. Dedicated storage nodes form a second cluster that provides all vSAN capacity. Dedicated compute nodes form a third cluster that runs all VM workloads.

When to Choose UCI

Scenario	Why UCI Works
Large environments (10+ nodes)	Independent scaling avoids over-provisioning
Storage-heavy workloads	Add storage capacity without buying compute you don’t need
Compute-heavy workloads	Add GPU or high-CPU nodes without buying storage you don’t need
AI / HPC / GPU clusters	Dedicated compute cluster with GPU passthrough, separate from storage
Cloud service providers	Optimize hardware spend per resource tier across many tenants
Predictable, uneven growth	Storage and compute demands grow at different rates

Key Characteristics

• Minimum: 6 nodes (2 controllers + 2 storage + 2 compute)
• Scaling: Add nodes to individual clusters independently
• Node roles: Each node has a single role (controller, storage, or compute)
• Cluster count: 3 (controller, storage, compute)
• Flexibility: Right-size hardware per role (NVMe-dense for storage, GPU-equipped for compute)

Hybrid: The Middle Ground

VergeOS also supports a hybrid model that sits between pure HCI and full UCI. In this topology, the controller nodes form an HCI cluster (providing both storage and compute), while a second cluster of dedicated compute nodes adds additional processing capacity.

This is useful when you have a solid HCI foundation but need to scale compute without adding more storage.

HCI vs UCI Comparison

Aspect	HCI	UCI
Minimum nodes	2	6
Cluster count	1	3
Node types	All nodes identical	Controller, storage, compute
Storage scaling	Tied to compute	Independent
Compute scaling	Tied to storage	Independent
Hardware uniformity	All nodes have same specs	Nodes optimized per role
Deployment complexity	Lower	Higher
Cost at small scale	Lower (fewer nodes)	Higher (minimum 6 nodes)
Cost at large scale	Can over-provision	Optimized spend per tier
Best fit	Small-to-medium, balanced	Large, uneven growth, specialized workloads

Decision Framework

Use this flowchart to guide your deployment model recommendation:

Quick Rules of Thumb

1. Start with HCI unless you have a specific reason to go UCI
2. Consider UCI when you need 10+ nodes or have specialized hardware requirements
3. Hybrid is a good stepping stone — start HCI, add compute-only nodes later
4. You can evolve from HCI to hybrid to UCI as the environment grows

Terraform Playground Examples

The VergeOS Terraform Playground includes example configurations for each deployment model, making it easy to test each topology:

Model	Example File	Nodes	Clusters
2-Node HCI	examples/2-node-hci.tfvars	2	1
HCI + Scale-Out	examples/4-node-hci.tfvars	4	1
Hybrid (HCI + Compute)	examples/4-node-hybrid-hci-2-cluster.tfvars	4	2
Full UCI	examples/6-node-uci-3-cluster.tfvars	6	3

Each example is a .tfvars file that you copy to terraform.tfvars and customize with your environment settings. The deployment model is controlled by boolean toggle variables:

• HCI: No toggles needed (default)
• HCI + Scale-Out: create_scale_out_nodes = true
• Hybrid: create_compute_nodes = true
• UCI: create_storage_nodes = true and create_compute_nodes = true

VMware Bridge

VMware vSAN only supports a hyperconverged model — every host in a vSAN cluster contributes both storage and compute. If you need to scale storage independently in a VMware environment, you must add an external SAN or NAS, breaking the HCI model entirely.

VergeOS UCI has no direct VMware equivalent. It lets you scale storage and compute independently while staying within a single platform — no external storage arrays needed. Think of it as if you could have a vSAN cluster where some hosts only provide storage and others only run VMs, all managed from one vCenter.

If a VMware customer says “we keep buying hosts just for storage capacity but don’t need the compute,” UCI is the answer.

Summary

Concept	Key Takeaway
HCI	Every node does everything. Simple, cost-effective at small scale.
UCI	Dedicated roles per node. Flexible, cost-optimized at large scale.
Hybrid	HCI foundation with compute-only expansion. A practical middle ground.
VergeOS advantage	Same platform supports all three models — no product changes needed.

Next Steps

Now that you understand HCI and UCI deployment models, the next topic covers the storage layer that powers both: vSAN / VergeFS →