Difference between Citrix Xen and VMware ESX

Comparison between Citrix Xen Server and VMware ESX 4.0


1) System Architecture

VMware ESX



Ø ESX’s approach to virtualization can best be described as binary translation: each OS request to the processor is intercepted and translated into a virtualization-friendly instruction.


Ø As the first layer of software interacting with the hardware, VMware has made considerable investments in the development of proprietary device drivers to support the variety of network and storage hardware available on commercial servers. As new hardware devices become available, VMware-specific drivers need to be written to support them.

Ø VMware ESX is designed to leverage hardware virtualization assist technologies, available on today’s Intel and AMD™ processors (Intel VT and AMD-V) including predates Virtulization-aware operating systems (Including Linux Distributions and Windows server 2008)


Citrix XenServer



Ø With XenServer, all virtual machine interactions with the hardware are managed through the Domain 0 control domain, which itself is a spe­cially privileged virtual machine running on top of the hypervisor

Ø Domain 0 runs a hardened, optimized instance of Linux. It’s important to recognize that to the administrator, Domain 0 is part of the overall XenServer system and requires no additional installation or management.

Ø XenServer is designed to leverage hardware virtualization assist technologies, available on today’s Intel and AMD™ processors (Intel VT and AMD-V) but does not support Virtulization aware OS (Windows Server 2008)


2) Installation, configuration and administration


Citrix XenServer

Ø XenServer has a straightforward installation process, often referred to as the 10 minutes to Xen experience. XenServer is installed on the host systems using a CD or network-based installation process. The XenCenter GUI-based administration console is then installed on any Windows PC or server. System configuration information is kept in an internal data store within the XenServer control domain and is replicated across all servers that are managed together (forming a resource pool) to maintain high availability of the core management services. As a result of this architecture, a separate database server is not required for the core management functions.

VMware ESX

Ø VMware ESX hypervisor is installed on the host servers. VMware uses vCenter Server for multi-server management and configuration. vCenter Server runs as a Windows service on a separate management server and requires a third-party database for storage and management of host system configurations. For redundancy and availability of the core management services, VMware recommends the addition of clustering software such as its vCenter Server Heartbeat add-on product.


3) Guest OS support

Citrix XenServer and VMware ESX

Ø VMware and XenServer both support the most popular Windows and Linux OSs, including Windows XP, Windows Vista®, Windows 2000 Server, Windows Server 2003, Windows Server 2008, Red Hat Linux, SUSE Linux and others. In addition, VMware ESX supports some flavors of BSD®, Sun™ Solaris™ and Novell Netware®. VMware and XenServer are both certified for Windows according to the requirements of the Microsoft Server Virtualization Validation Program (SVVP).


4) Storage integration

VMware ESX

Ø VMware typically leverages its proprietary VMFS file system for storage, although raw disk options are available. VMFS is the default storage system for VM files, with both local and shared (SAN or NAS) storage. VMFS is a clustered file system that enables advanced features such as VMotion and Storage Vmotion

Citrix XenServer

Ø XenServer does not impose its own file system on storage systems but, instead, leverages the native storage capabilities more directly. For example, with a file-based shared storage system such as NFS, XenServer VMs are stored directly using Microsoft VHD (Virtual Hard Disk) format.



5) Performance

Ø VMware and ESX server has almost same performance in all use case scenarios.


6) Virtual machine backup and recovery


· Citrix XenServer

Ø XenServer and VMware both offer VM snapshot capability for basic backup and recovery needs. Support for traditional agent-based backup solutions is also available and both vendors maintain ecosystem partnerships with a variety of backup software providers

VMware ESX

Ø VMware offers a feature called Data Recovery in vSphere for backup of virtual machines. Data Recovery is a plug-in for vCenter Server that schedules regular disk snapshots for virtual machines.



7) VM load management

· Citrix XenServer

Ø XenServer includes a feature called Workload Balancing (WLB). Workload Balancing captures data such as CPU, memory, disk I/O and network I/O on the hosts and virtual machines to guide the initial and ongoing host location for virtual machines. There are two optimization modes for WLB: optimize for performance and optimize for density. Optimizing for performance ensures that minimum performance thresholds are maintained, whereas optimizing for density ensures reduced power consumption by placing VMs on the minimum number of hosts.

VMware ESX


Ø VMware offers DRS, a feature that guides the initial VM placement as well as semi- or fully-automated load management of VMs using its Distributed Resource Scheduler (DRS) feature. DRS does not enable much customization of the load management algorithm and is based solely on CPU and memory utilization.

8) System Maintenance


Citrix XenServer

Ø VMware’s product includes automated patching for the hypervisor as well as guest OS. As a complex and sophisticated software system, VMware requires significantly more patching and updates than other system software such as the BIOS or device drivers. the automated update process is touted by VMware as a way of managing the application of these updates.

· Citrix XenServer

Ø XenServer does not include patching features for guests, instead, leaving this task for the variety of products from OS vendors (and their ecosystem partners) or the provisioning services feature of the product.


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