Hyper-converged infrastructure (HCI) collapses compute, storage, and networking into a single software-defined layer running on commodity x86 servers. It eliminates the traditional three-tier architecture (separate compute servers, Fibre Channel SAN, and top-of-rack switches) in favour of a distributed data fabric across the cluster nodes. For on-premises deployments with 3–20 nodes, HCI typically delivers better performance, simpler operations, and lower total cost of ownership than equivalent three-tier alternatives.
VMware vSAN (now branded as vSAN/VCF — VMware Cloud Foundation) and Nutanix AOS are the two dominant enterprise HCI platforms. They share the same fundamental concept but differ in architecture, resiliency model, and operational philosophy.
Architecture Overview
VMware vSAN
vSAN is tightly integrated with vSphere. It pools the local storage (NVMe, SAS SSD, SAS HDD) across vSphere hosts into a shared datastore presented as a vSAN Datastore consumed by VMs. The storage policy engine (SPBM — Storage Policy Based Management) controls how each VM's data is protected.
- Cluster minimum: 3 hosts for standard cluster; 2-node cluster with witness appliance for ROBO deployments
- Data distribution: Objects (VM home namespace, VM swap, virtual disk) are striped and replicated across hosts according to the storage policy (RAID-1 mirror or erasure coding RAID-5/6)
- Witness host: For stretched clusters (two sites), a third-site witness VM mediates quorum without storing data
- Disk group design: Each host has one or more disk groups, each with a cache tier (NVMe/SSD) and capacity tier (SSD or HDD). Losing a host's cache tier is non-fatal; the SSD cache is write-through to capacity after each I/O anyway in recent versions.
Nutanix AOS
Nutanix runs the AOS (Acropolis Operating System) software stack, which includes the Controller VM (CVM) on each node — a Linux-based VM that handles all storage I/O for the node. AHV (Acropolis Hypervisor, based on KVM) is the native hypervisor, but AOS supports ESXi and Hyper-V as well.
- Cluster minimum: 3 nodes
- Data distribution: Nutanix uses a distributed data fabric where data is split into "extents" and distributed with replication factor (RF2 or RF3) across nodes. Erasure coding (EC-X) is available for cold data.
- CVM isolation: The CVM handles I/O locally; if remote storage is needed, the VM communicates with the CVM on another node. This means Nutanix doesn't rely on a shared network fabric for storage in the same way vSAN does — local reads are always local.
- Prism Central: The management layer (Prism) has a much more polished UI than vCenter for storage operations; cluster expansion is largely automated.
Resiliency Model Comparison
| Factor | vSAN | Nutanix AOS |
|---|---|---|
| Resiliency policy | SPBM policy per object (FTT=1 RAID-1, FTT=1 RAID-5, etc.) | RF2 (1 failure) or RF3 (2 failures) cluster-wide |
| Node failure tolerance (3-node cluster) | FTT=1 RAID-1: 1 node failure | RF2: 1 node failure |
| Erasure coding | RAID-5 (4 nodes min), RAID-6 (6 nodes min) | EC-X: 4 nodes min for 2+1, 6 nodes for 4+2 |
| Rebuild after failure | Object re-syncs across remaining hosts; no dedicated spare needed | Extent re-replicates across remaining nodes; no spare needed |
| Granularity | Per-VM storage policy (different VMs can have different protection) | Cluster-wide RF setting (mixed RF requires multiple containers) |
Networking Requirements
Both platforms require a dedicated storage/vSAN/AHV backplane network. Minimum 10 GbE; 25 GbE recommended for all-flash clusters. RDMA (RoCE v2) is supported by vSAN and improves I/O latency and CPU efficiency for NVMe-oF workloads.
Nutanix is generally less prescriptive about network design — it works well on standard Ethernet with proper MTU settings (jumbo frames, MTU 9000). vSAN has stricter requirements and is more sensitive to misconfigured network settings (multicast for witness, latency between witness and data sites for stretched clusters).
Operational Considerations
- Licensing: vSAN licensing is per-CPU socket, often bundled into VMware Cloud Foundation. Post-Broadcom acquisition, vSAN pricing has increased significantly. Nutanix licenses on a per-node capacity basis with a subscription model.
- Hypervisor lock-in: vSAN requires vSphere; you cannot run AHV or Hyper-V on a vSAN cluster. Nutanix AOS supports multiple hypervisors, making it easier to transition if needed.
- Upgrade experience: Nutanix LCM (Life Cycle Manager) is widely praised for enabling rolling upgrades with near-zero downtime. vSphere upgrades with vSAN require careful sequencing and are more complex.
- Cluster expansion: Both support adding nodes to a running cluster (scale-out). Nutanix handles rebalancing automatically; vSAN may require policy re-application on some objects.
"vSAN is the right answer if you're deeply invested in VMware and need per-VM storage policy flexibility. Nutanix is the right answer if you want the best operational experience and don't want to be locked into a single hypervisor vendor."
Which to Choose
- Choose vSAN/VCF if: existing vSphere expertise, need RAID-5/6 at smaller cluster sizes, require vSphere-specific features (vGPU via vSphere, vSphere Replication, SRM)
- Choose Nutanix AOS/AHV if: want best-in-class operational tooling, need multi-hypervisor flexibility, concerned about VMware/Broadcom licensing trajectory, want a single vendor for compute+storage+management
Sripadatech designs and deploys HCI environments using both vSAN and Nutanix platforms. Contact us for a workload sizing and platform recommendation.