Based on recent research and my experience using Proxmox VE as well as previous experience with XenServer, this article provides an analysis and comparison of two of the most popular open-source hypervisors: Proxmox VE and XenServer. This analysis focuses on their advantages in virtual machine resource allocation, supported virtualization methods, server architecture, virtual machine capacity, host and guest OS compatibility, and management features. Both of these open-source virtualization solutions are widely used around the world for providing enterprise-level user experiences similar to VMware products. The shift toward open-source virtualization management has transformed how businesses manage computing resources, reducing IT operational costs while improving performance and flexibility. Although there are other excellent open-source products available in China, such as ZStack, which offer comparable user experiences, they currently do not match these two platforms in terms of enterprise-level functionality and openness, and therefore are not included in this comparison.

Introduction to Hypervisors

Hypervisors are the core platform for adopting and investing in virtualization technologies. The most widely used open-source virtualization kernels today include Xen, KVM, LXC, and Docker. These virtualization kernels rely on a single server’s hardware and system, and require a hypervisor to manage, orchestrate, and pool resources across hardware clusters in large-scale environments. Therefore, the capacity, compatibility, user experience, and performance of a hypervisor are critical in addressing the challenges faced by operators in managing virtualized infrastructures. In this regard, OpenStack, which is an open-source management program, has been less user-friendly. As a result, hypervisors specifically designed to address these pain points have gained significant popularity. Moreover, while virtualization technology has led to a sharp decrease in costs, open-source virtualization management systems further lower IT investment and operational expenses. After a period of refinement, Proxmox VE and XenServer have become the most popular and user-friendly open-source virtualization platforms.

Proxmox VE Overview

Proxmox VE (Proxmox Virtual Environment) is an open-source virtualization solution that provides computing, networking, and storage in a single package. Proxmox VE supports both virtual machines (VMs) and containers, offering a flexible and versatile virtualization platform. Developed based on Debian Linux, Proxmox VE is fully open-source and supports both KVM (for virtual machines) and LXC (for containers) virtualization technologies.

XenServer Overview

XenServer is an open-source virtualization platform based on the Xen project, which was later acquired by Citrix and commercialized as XenServer before transitioning back to open-source development. XenServer primarily relies on the Xen hypervisor to build its virtualization management stack. It is widely used in enterprise production environments, backed by Citrix product bundling and AWS cloud services that use Xen.

Among the open-source virtualization management products available today, Proxmox VE and XenServer are the most prominent due to their long history, stable version iteration, and practical use in various production environments. These two products exhibit many similarities, and this article provides a detailed comparison to help users select the most suitable virtualization management program based on factors such as virtualization requirements, organizational scale, personnel skills, and computational workloads.

Virtualization Methods Supported

Virtualization technologies can generally be divided into full virtualization, paravirtualization, OS-level virtualization, and hardware-assisted virtualization. From the perspective of supported virtualization methods, Proxmox VE and XenServer differ in the technologies they support:

Proxmox VE supports full virtualization, hardware-assisted virtualization (via KVM), and OS-level virtualization (via LXC).

XenServer supports full virtualization, paravirtualization, and hardware-assisted virtualization.

For XenServer, while hardware-assisted virtual machines require an x86 CPU with Intel VT-x or AMD-V, paravirtualization does not require processor virtualization support. Instead, it modifies the guest OS kernel, which differs from how Proxmox VE (using KVM) implements virtualization. Proxmox VE also supports OS-level virtualization, which is uncommon in Type 1 hypervisors. Most Type 1 hypervisors today support paravirtualization and hardware-assisted virtualization, but full virtualization can suffer from performance issues due to the need for binary translation, which is time-consuming and can lead to high overhead.

Paravirtualization overcomes the performance issues of full virtualization, offering 80% to 97% of the host’s performance on x86 architectures. However, since paravirtualization requires modifying the OS kernel, it does not support Windows operating systems. XenServer’s support for paravirtualization offers significant performance benefits for Linux-based OSes, but it is not applicable to Windows.

Hardware-Assisted Virtualization

Both Proxmox VE and XenServer support hardware-assisted virtualization, which offloads some virtualization tasks to the hardware, improving performance. For instance, AWS’s Nitro architecture decouples networking, storage, security, and monitoring from traditional VMs and moves these tasks to dedicated hardware, enhancing efficiency and speed. The Nitro system uses custom ASICs to perform tasks previously handled by software, allowing for faster and more efficient resource allocation, and enabling servers to deliver high-speed performance across IO modules.

With the development of open-source hardware projects like OCP and Scorpio, it is possible that virtualization management programs like Proxmox VE and XenServer could also benefit from specialized, modular hardware. However, today’s focus is on practical solutions that meet user needs in modern virtualized IT infrastructures.

Virtualization Host and OS Support

Both Proxmox VE and XenServer primarily support x86_64 architecture CPUs and do not support Power or other CPU architectures. Although Xen and KVM (the underlying virtualization engines) are compatible with other architectures like Power or MIPS (as seen with domestic Chinese Loongson CPUs), neither Proxmox VE nor XenServer has specifically integrated or adapted their management tools for these architectures.

In terms of supported guest operating systems, Proxmox VE is the only Type 1 open-source hypervisor that efficiently collaborates with all major guest operating systems. XenServer, on the other hand, does not officially support FreeBSD, NetBSD, or any other BSD variants as guest operating systems. Users may try to install FreeBSD as a HVM (Hardware Virtual Machine) guest, but performance is limited due to simulated IO. For FreeBSD and other BSD systems, a dedicated hypervisor like bhyve is a better option.

Virtual Machine Capacity

Both Proxmox VE 5.x and XenServer 7.x support high virtual machine capacity, with each offering scalability in terms of the number of VMs that can be managed. XenServer 7 can manage up to 500 VMs, with this number increasing to 650 for Linux-based guests. The number of VMs supported can change based on performance baseline and VM configuration. Proxmox VE offers similar scalability, but it is more flexible when it comes to resource allocation.

XenServer supports up to 32 virtual CPUs (vCPUs) per VM and uses a fair share algorithm for CPU resource balancing, which ensures load balancing across physical CPU resources. XenServer also allows dynamic CPU allocation, which optimizes CPU usage as needed. Proxmox VE supports up to 160 vCPUs per VM and allows up to 192GB of RAM for a single VM. Both platforms support dynamic memory control and the hot-plugging of CPU, memory, network, and storage resources.

Networking Features

XenServer supports a maximum of seven virtual NICs per VM, though this can vary based on the guest OS. In contrast, Proxmox VE, which is built on Debian, supports far more network interfaces per VM. Both Proxmox VE and XenServer use Linux Bridge and Open vSwitch to provide fair network I/O resources and QoS control for VMs. While XenServer’s network features are more robust, many of its advanced network functionalities are available only in the commercial version, whereas both platforms offer similar network management features in their open-source versions.

Storage I/O and Backup

XenServer supports up to 16 virtual disks per VM, though this can vary based on the guest OS. Storage resources in XenServer are managed using a fair-share method based on defined priority settings. Proxmox VE supports a variety of storage solutions, including local directories, LVM for iSCSI targets, NFS for file-based storage, GlusterFS, and Ceph for distributed storage. For backup, Proxmox VE typically uses FreeNAS, though local and CephFS backups are also supported.

Management Features

Both Proxmox VE and XenServer offer similar management features, such as asset management, snapshotting, high availability, live migration, performance metrics, storage migration, VM cloning, capacity planning, virtual firewalls, and backup/restore capabilities. However, the way these features work can differ significantly between the two platforms.

XenServer’s GUI management is based on a client-server architecture, where the GUI client is installed on a Windows machine and communicates with the XenServer host over SSL encryption. Proxmox VE, in contrast, uses a web-based HTML5 GUI that is accessible from any browser, providing a more modern and versatile approach to management. Both platforms also offer command-line management tools.

VM Import/Export and Migration

XenServer excels in VM import/export capabilities, supporting the open virtualization format (OVF) for importing and exporting VMs between homogeneous and heterogeneous environments. This feature is particularly useful for migrating VMs from other hypervisors like VMware and Hyper-V. Proxmox VE does not offer a dedicated GUI for importing/exporting VMs, but supports VM imports via CLI tools for formats like qcow2, raw, and vmdk.

Conclusion

While both Proxmox VE and XenServer offer robust open-source virtualization management solutions, the main difference lies in Proxmox VE’s support for Linux containers (OS-level virtualization), which enhances its flexibility compared to XenServer. Despite these differences, both platforms are capable of managing large-scale, multi-tenant virtualization environments and are suitable for diverse workloads. The choice between the two will largely depend on the specific needs of an organization, with Proxmox VE being ideal for container-based environments, and XenServer providing excellent support for Windows and Linux workloads in high-demand, enterprise production environments.