HCI vs UCI: Deployment Models

Understand the two VergeOS deployment architectures -- Hyperconverged Infrastructure (HCI) and Ultra Converged Infrastructure (UCI) -- and when to recommend each.

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.

System vs. Cluster

• System — the entire VergeOS deployment, made up of one or more clusters managed as a single unit.
• Cluster — a group of nodes with matching hardware that share compute and high-availability boundaries. vSAN storage tiers span all clusters in the system, so storage is shared system-wide even though compute and HA are scoped per cluster.

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 most common starting point 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 workload tier 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
• Node roles: All nodes run storage and compute
• Cluster count: 1
• Simplicity: Easiest to deploy and manage

UCI: Ultra Converged Infrastructure

UCI is the umbrella term for any deployment where storage and compute scale independently on dedicated node types. The canonical form uses three clusters (controller, storage, compute); a popular hybrid variant collapses controller + storage into two clusters. Either way, 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 in the canonical form (controller, storage, compute); 2 in the hybrid variant
• Flexibility: Right-size hardware per role (NVMe-dense for storage, GPU-equipped for compute)

Hybrid UCI: The Two-Cluster Variant

VergeOS also supports a hybrid UCI model — a two-cluster UCI variant that collapses the controller and storage roles into one cluster. Controller nodes provide vSAN storage AND system management; they do not run production VM workloads. A separate cluster of dedicated compute nodes handles all VM execution.

This is a popular deployment model because it keeps the controller/storage layer lean and dedicated, while compute scales independently via its own cluster. The controllers provide vSAN storage to the compute nodes over the core fabric.

Controller nodes don't have to run VMs

In a hybrid deployment, controller nodes commonly serve only as storage and management nodes — no production VMs run on them. This reduces resource contention on the controllers and simplifies capacity planning: storage scales by adding nodes to the controller cluster, compute scales by adding nodes to the compute cluster.

Alternatively, the controllers can also run VMs alongside storage if needed — this is useful in smaller environments where dedicating two nodes purely to storage feels wasteful. The hybrid model is flexible: controllers can provide storage-only, or storage + compute, depending on your requirements.

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 UCI (2-cluster) is a good stepping stone -- start HCI, then split compute onto its own cluster
4. You can evolve from HCI to hybrid UCI to full 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 UCI	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 UCI: create_compute_nodes = true
• UCI: create_storage_nodes = true and create_compute_nodes = true

VMware Bridge

Coming from vSAN? VergeOS supports both HCI and UCI deployments from the same install — no separate product tier or licensing for disaggregated storage. Storage-only and compute-only node types are first-class deployment options, all managed from the same UI.

Nutanix Bridge

Coming from Nutanix? VergeOS runs storage as an integrated OS service — there is no per-node CVM to size, patch, or troubleshoot. Storage-only and compute-only node types let you dedicate hardware per role within a single system.

Single-Node Deployments

While VergeOS is designed for multi-node clusters, single-node deployments have valid use cases:

• Bare-metal replacement — Replace a traditional physical server with a single VergeOS node running multiple VMs, gaining the benefits of virtualization (snapshots, resource management, easy backup) without needing a second node
• Edge sites — A single node at a remote location where data is not critical locally (e.g., thin client host, local cache, signage) and can be replicated from a central site if needed
• Development / lab — A standalone system for testing and development

Single-node deployments still have disk-level redundancy — vSAN uses 2-copy mirroring across drives within the node (yielding ~50% usable capacity), protecting against individual drive failures. However, there is no node-level redundancy — if the node itself fails, workloads are down until it is restored. Snapshots and off-site replication are strongly recommended.

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 UCI	Controllers handle storage/management; compute scales separately. Two-cluster UCI variant.
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 →