Migrating from a proprietary virtualization environment like VMware to an open-source solution such as Proxmox VE is a complex undertaking, especially in enterprise contexts and even more so within a public sector organization. It’s not merely about replacing one software with another; it involves re-evaluating processes, skill sets, and long-term strategies. The preliminary assessment phase is the cornerstone for the entire project’s success, often revealing numbers and details that can surprise even seasoned teams.
When an organization with 2,000 endpoints and hundreds of virtualized VMs decides to embark on this journey, the motivations are manifold: from constantly increasing licensing costs to the pursuit of greater flexibility and control over the infrastructure. The objective is clear: reduce operational expenses, improve resilience, and prepare for future technological evolutions. However, before moving a single bit, a surgical analysis of the existing environment is indispensable. A real, anonymized inventory revealed that a significant portion of VMs were decommissioned or could be consolidated, a fact that greatly simplified planning and reduced the load on the Proxmox environment.
Tested on: VMware vSphere 6.7/7.0 · Proxmox VE 8.2 · September 2026
Prerequisites / Test Environment
The reference environment for this analysis is an infrastructure with:
- VMware vSphere: 15 ESXi hosts (6.7 and 7.0) managed by vCenter Server.
- Virtual Machines: Over 300 production VMs, with mixed operating systems (Windows Server 2008 R2 to 2022, various Linux distributions).
- Storage: 50 TB of shared storage (Fibre Channel SAN and iSCSI).
- Networking: Cisco and FortiGate network infrastructure with various VLANs dedicated to services and test/production environments.
- Personnel: Internal IT team with consolidated VMware expertise, but limited experience with Proxmox VE.
The initial approach involved collecting detailed data via vCenter, PowerCLI scripts, and interviews with application service managers. This allowed for the creation of a precise and functional inventory, crucial for subsequent decisions.
1. VM Inventory and Consolidation
The first and most critical phase was the creation of a complete and accurate inventory. A simple list of VMs is not enough; detailed information on each virtual machine is required:
- Operating System: Version, patch level.
- Applications: Installed services, dependencies, owners.
- Assigned Resources: vCPU, RAM, Storage (VMDK/VHDX).
- Actual Usage: Historical data on CPU, RAM, disk I/O, and network usage (collected via vCenter Performance Charts or external tools).
- Owner/Manager: Who is the contact person for the VM and its service.
- Status: Production, test, development, decommissioned, to be consolidated.
Analysis of actual usage revealed that a significant portion of VMs were over-provisioned or no longer active. For example, 25 Windows Server 2008 R2 VMs had been ‘powered off’ for over a year, and another 15 were test or development VMs with excessive resources. This led to the identification of 40 VMs that could be consolidated or eliminated before migration, reducing the load and complexity of the new Proxmox environment. Read also: Fail2ban on Linux: Complete Setup and SSH Hardening
To extract basic data from vCenter, a PowerCLI script was used:
Connect-VIServer -Server your_vcenter_ip
Get-VM | Select Name, PowerState, NumCpu, MemoryGB, ProvisionedSpaceGB, UsedSpaceGB, `
@{N='OSFullName';E={$_.Guest.OSFullName}}, `
@{N='IPAddress';E={$_.Guest.IPAddress[0]}} | Export-Csv -Path "C:\VM_Inventory.csv" -NoTypeInformation
Disconnect-VIServer2. Cost Analysis and ROI
One of the primary drivers for the migration was the cost of VMware licenses. With increasing prices and changes in the licensing model (especially with the Broadcom acquisition), the annual virtualization budget had become unsustainable for the public sector organization. The analysis estimated annual savings of over €100,000 just for VMware licenses, which could be reinvested in training, hardware, or other security priorities. Read also: NIS2 Compliance: 6-Month Review, Operational Insights
This saving does not include indirect costs, such as simplified management and increased flexibility offered by an open-source platform, which reduces vendor lock-in. The transition to Proxmox VE is not just a technological change but an opportunity to reallocate financial resources towards innovation and security.
3. Application Dependencies and RTO/RPO
Mapping application dependencies was crucial. Each VM was associated with the services it hosts and other VMs/services it depends on. This allowed for the creation of a critical application flow diagram, identifying the Recovery Time Objective (RTO) and Recovery Point Objective (RPO) for each service.
For the most critical services, the possibility of implementing Proxmox’s native high availability (HA) and disaster recovery (DR) solutions, such as Proxmox HA and Proxmox Backup Server, was evaluated. This allowed for recalibrating RTO and RPO, often improving them compared to the existing VMware environment, thanks to tighter integration between hypervisor and backup.
Common Errors and Troubleshooting
One of the most common errors in this phase is underestimating inventory complexity. A superficial list leads to surprises during migration. Ensure you:
- Verify actual status: Don’t just rely on ‘powered off’ in vCenter. Access the VMs and verify that no active services or critical data exist.
- Interview stakeholders: Often, only end-users or application owners know the real dependencies and importance of a VM.
- Do not neglect storage: Analyzing occupied storage and, especially, allocated but unused storage (thin provisioning) is crucial for correctly sizing the new environment.
FAQ — Frequently Asked Questions
How long does the analysis phase take for a migration of this scale?
For an environment with 300+ VMs, the analysis phase can take 1 to 3 months, depending on team availability, the quality of existing documentation, and the complexity of application dependencies. It’s a time investment that pays off in terms of risk reduction and migration smoothness.
What are the main risks of an insufficient analysis phase?
Risks include unexpected service outages, data loss, higher-than-expected migration costs, over- or under-sizing the new environment, and team frustration. Insufficient analysis is the primary cause of failure for complex migration projects.
Is it necessary to involve all departments in this phase?
Yes, it is essential to involve all departments that use virtualized services. Even if the IT team manages the infrastructure, application owners and end-users know the importance and criticality of services. Their collaboration is essential for accurate mapping and defining realistic RTO/RPO.
How are VMs with outdated operating systems (e.g., Windows Server 2008 R2) managed?
VMs with outdated OSes represent a significant security risk. During the analysis, it is a priority to identify these VMs and plan an upgrade or decommissioning. If migration is unavoidable, it is advisable to isolate them in a dedicated VLAN and apply additional hardening, as suggested by official security guidelines.
Conclusions with Operational Takeaways
Migrating from VMware to Proxmox VE in an enterprise context, especially in a public sector organization, is a strategic operation that requires meticulous planning. The preliminary assessment phase is not optional but a mandatory step that ensures project success. A detailed inventory, cost analysis, and accurate mapping of application dependencies are the pillars upon which to build an efficient and smooth migration. Licensing savings and control over an open-source platform offer significant long-term benefits. Always start with the inventory, and don’t be afraid to decommission or consolidate what is no longer needed.
Sources
Updated: September 2026
