VMware ESXi | VirtualizationWorks.com

Overview:

VMware ESXi 3.5 is the next generation, OS-independent hypervisor that makes virtualization easy to deploy. Requiring minimal configuration, users can be up and running in minutes with a production class hypervisor that scales to run the most resource intensive applications.

Benefits

Reduce server deployment time with an easy to use and configure hypervisor.
Achieve unparalleled infrastructure reliability while minimizing security exposure.
Simplify management with a compact, OS-independent hypervisor.
Build a complete virtual infrastructure on the industry’s most robust platform.

What is VMware ESXi 3.5?

VMware ESXi 3.5 is the next generation, OS-independent hypervisor that makes virtualization easy to deploy. Requiring minimal configuration, users can be up and running in minutes with a production class hypervisor that scales to run the most resource intensive applications. Also available embedded in server hardware, VMware ESXi enables the plug-and-play data center with greater security, reliability and manageability.

How Does VMware ESXi Work?

Building on the legacy of the market-leading VMware ESX, a production proven, stable and mature hypervisor, VMware ESXi is the culmination of almost a decade of research into hypervisor design. VMware ESXi offers the same great performance and scalability in a compact, 32-MB package. (For a complete description of the features and capabilities of VMware ESX, please visit www.vmware.com/products/vi/esx/.)

At a fraction of the size of general purpose operating system, the 32-MB footprint of VMware ESXi sets a new bar for security due to a smaller “attack surface.” This small footprint and hardware-like reliability also enable VMware ESXi to be built directly into industry standard x86 servers. Customers can now deploy diskless servers attached to shared storage, removing the most failure prone server component, while decreasing power and cooling requirements.

VMware ESXi works with standards-based monitoring protocols and is easily managed one-to-one with the VMware Infrastructure Client. When licensed within a VMware Infrastructure edition, VMware ESXi supports VMware VirtualCenter and the VMware Infrastructure API for integration with 3rd-party software solutions.

Innovative, thin hypervisor architecture

Operating system-independent design optimized for virtualization performance.
Unmatched security with a small 32MB, virtualization-centric architecture.

Intuitive interfaces and intelligent defaults

Menu-driven start up experience and intelligent defaults that dramatically reduce deployment time—booting the server to running virtual machines takes just minutes.
Plug-and-play of server hardware that provides instant addition of resources for on-demand capacity.

Seamless Upgrade to VMware Infrastructure

Simple license upgrade to VMware Infrastructure to support centralized management with VirtualCenter and virtual infrastructure capabilities such as VMotion, Distributed Resource Scheduler, and High Availability (HA)

Features:

Below you will find a comprehensive list of the VMware ESXi features.

Key Features

Record-setting performance with up to 8,900 database transactions per second, 200,000 I/O operations per second, and up to 16,000 Exchange mailboxes on a single physical host
Up to eight-way virtual SMP (symmetric multiprocessing), enabling the virtualization of multiprocessor workloads* (8-way vSMP requires vSphere Enterprise Plus licensing)
Memory overcommittment and deduplication, allowing higher consolidation ratios
Broadest OS support of any hypervisor, enabling IT to virtualize numerous versions of Windows®, Linux®, Solaris®, NetWare®, and other operating systems.
Built-in high availability through NIC teaming and HBA multipathing to protect against hardware component failures
Up to 64 logical processing cores, 256 virtual CPUs, and 1TB RAM per host, enabling higher consolidation ratios

Architecture

Bare-metal, 64-bit hypervisor architecture. Achieve near-native virtual machine performance, reliability and scalability with production-proven hypervisor technology that runs directly on server hardware, without the need for a host operating system.
Virtual disk files. Use virtual machine disk (VMDK) files to provide virtual machines access to their own private datastores while giving IT administrators the flexibility to create, manage and migrate virtual machine storage as separate, self-contained files that can reside on shared storage equipment.
VMware vStorage VMFS. Eliminate single points of failure and balance storage resources by implementing shared storage for virtual machines with VMware vStorage Virtual Machine File System (“VMFS”), a cluster file system that allows multiple VMware ESX hosts to access a single VMDK file concurrently. VMFS is supported on a mix of Fibre Channel SAN, iSCSI SAN, and NAS storage arrays in a manner that is transparent to application owners and end users. Download the VMFS datasheet to learn more about VMFS, which provides new enhancements such as dynamic increase of VMFS volume size.
Boot from SAN. Eliminate the need to separately backup local attached server disks by running VMware ESX hosts on diskless configurations of blade and rack mount servers.
Virtual networking. The virtual networking capabilities in VMware ESX and ESXi allow customers to build complex networks between virtual machines residing on a single host or across multiple installations of VMware ESX and ESXi hosts for production deployments or development and testing purposes. Configure each virtual machine with one or more virtual NIC, each with its own IP and MAC address, to make virtual machines indistinguishable from physical machines. Create a simulated network within a VMware ESX host with virtual switches that connect virtual machines. Use virtual LANs (VLANs) to overlay a logical LAN on top of physical LANs to isolate network traffic for security and load segregation. Modify network configurations without having to change actual cabling and switch setups.

Advanced Resource Management

VMware ESX and VMware ESXi offers advanced resource management capabilities to improve performance and increase consolidation ratios.

Resource management for virtual machines. Define advanced resource allocation policies for virtual machines to improve service levels to software applications. Establish minimum, maximum and proportional resource shares for CPU, memory, disk and network bandwidth. Modify allocations while virtual machines are running.
Intelligent CPU virtualization. Manage the execution of virtual machine processes with intelligent process scheduling and load balancing across all available CPUs on the physical host.
RAM overcommitment. Increase memory utilization by configuring virtual machine memory that safely exceeds the physical server memory, enabling a greater number of virtual machines to run on a VMware ESX or ESXi host.
Transparent page sharing (memory de-duplication). Use physical RAM more efficiently by storing memory pages identical across multiple virtual machines only once.
Memory ballooning. Shift RAM dynamically from idle virtual machines to active workloads. Memory ballooning artificially induces memory pressure within idle virtual machines, forcing them to use their own paging areas and release memory for active virtual machines.
Network traffic shaping. Ensure that critical virtual machines receive priority access to network bandwidth. Network traffic from virtual machines can be prioritized on a “fair share” basis. Network Traffic Shaper manages virtual machine network traffic to meet peak bandwidth, average bandwidth and burst size constraints.
Storage I/O traffic prioritization. Ensure that critical virtual machines receive priority access to storage devices by prioritizing I/O traffic on a “fair share” basis.
Improved power management. Improve energy efficiency with dynamic voltage and frequency scaling and support for Intel SpeedStep® and AMD PowerNow!.

Performance and Scalability

VMware ESX and VMware ESXi deliver unparalleled performance and scalability, enabling even the most resource intensive production applications to be virtualized.

Performance optimizations for virtualized workloads. VMware ESX and ESXi 4.0 have undergone performance optimizations for specific business-critical applications such as Oracle databases, Microsoft SQL Server, and Microsoft Exchange. Get up to 8,900 database transactions per second, 200,000 I/O operations per second, and up to 16,000 Exchange mailboxes per host.
Performance improvements for iSCSI storage. Leverage a combination of new in-guest virtualization-optimized SCSI drivers and VMkernel-level storage stack optimizations to dramatically increase performance for I/O-intensive applications such as databases and messaging applications.
Support for powerful server hardware. Take advantage of hardware systems with up to 64 physical CPU cores, 256 virtual CPUs, 1TB RAM, and up to hundreds of virtual machines on a single host to facilitate large-scale consolidation and disaster recovery projects.
Support for larger virtual machines. Configure virtual machines with as much as 255GB RAM.
Support for eight-way virtual SMP. VMware Virtual Symmetric Multiprocessing (SMP) enhances virtual machine performance by enabling a single virtual machine to use up to eight physical processors, simultaneously. VMware Virtual SMP enables virtualization of the most CPU-intensive enterprise applications such as databases, ERP and CRM.
Raw device mapping. Optionally, map SAN LUNs directly to a virtual machine in order to enable application clustering and array-based snapshot technology while profiting from the manageability benefits of VMware vStorage VMFS.
Support for hardware virtualization. VMware ESX and ESXi provide industry-leading support for next-generation virtualization hardware assist technologies such as AMD’s Rapid Virtualization Indexing® or Intel’s Extended Page Tables.
Support for large memory pages. VMware ESX and ESXi are the only hypervisors that support large memory pages to improve efficiency of memory access for guest operating systems.
Networking performance optimizations. VMware ESX and ESXi support a variety of performance offload technologies including TCP Segmentation Offloading (TSO), VLAN and checksum offloading, and jumbo frames to reduce the CPU overhead associated with processing network I/O. Additionally, virtualization optimized I/O performance features such as NetQueue is supported which significantly improves performance in 10 Gigabit Ethernet virtualized environments.
Support for new high performance devices and protocols: VMware ESX and ESXi support 10Gb Ethernet network cards and storage arrays and Infiniband technology to improve virtual machine performance.
Support for paravirtualization. VMware ESX and ESXi support para-virtualized Linux guest operating systems (Linux kernel 2.6.21 onwards) to improve virtual machine performance.
VMDirectPath I/O for virtual machines. Enhance CPU efficiency for applications that require frequent access to I/O devices by allowing select virtual machines to directly access underlying hardware devices. Other virtualization features, such as VMware VMotion™, hardware independence and sharing of physical I/O devices will not be available to the virtual machines using this feature.

High Availability

VMware ESX and ESXi delivers datacenter-class high availability for virtual machines.

Built-in storage access multipathing. Ensure shared storage availability with SAN multipathing for Fibre Channel or iSCSI SAN.
NIC teaming. Give each networked virtual machine built-in NIC failover and load balancing enabling greater hardware availability and fault tolerance. NIC teaming policies allow users to configure multiple active and standby adapters.
Support for Microsoft Clustering Services. Cluster virtual machines running Microsoft Windows operating system across physical hosts.

Interoperability

VMware ESX and VMware ESXi are optimized, rigorously tested and certified across the complete IT stack of servers, storage, operating systems, and software applications allowing for enterprise-wide standardization.

Server hardware. VMware ESX and ESXi have been certified with industry-leading rack, tower and blade servers from Dell, Fujitsu Siemens, HP, IBM, NEC, Sun Microsystems and Unisys.
Storage hardware. VMware ESX and ESXi are certified with a wide range of storage systems from Dell, EMC, Fujitsu, Fujitsu Siemens, HP, Hitachi Data Systems, IBM, NEC, Network Appliance, StorageTek, Sun Microsystems and 3PAR. Internal SATA drives, Direct Attached Storage (DAS), Network Attached Storage (NAS) and both fibre channel SAN and iSCSI SAN are supported.
Operating systems. VMware ESX and ESXi support the broadest range of unmodified operating systems, including Windows, Linux, Solaris, Novell NetWare and more. VMware recently added support for 20 new guest operating systems.
Software applications. Run any software application in VMware virtual machines without the need to modify the application.
Virtual machine formats. VMware ESX and ESXi can run virtual machines created in non-VMware formats. Using the free VMware vCenter Converter, users can convert and run Microsoft Virtual Server and Virtual PC, and Symantec LiveState Recovery virtual machines on VMware ESX and ESXi hosts.

Security

Advanced security features in VMware ESX and ESXi protect stored data within the virtual environment.

VMware VMsafe. VMware VMsafe is a new security technology that helps protect virtualized workloads in ways previously not possible with physical machines. VMsafe provides a set of security APIs that enable third-party security products to gain the same visibility as VMware ESX or ESXi into the operation of a virtual machine to identify and eliminate malware, such as viruses, trojans and key-loggers. This advanced protection is achieved by fine-grained visibility into the virtual machine’s hardware resources such as memory, CPU and disk and its I/O systems.
VMkernel Protection. VMware ESX and ESXi are protected from common attacks and exploits by assuring the integrity of the VMkernel, a core component of the hypervisor. Disk integrity techniques in ESX and ESXi protect the boot-up of the hypervisor by utilizing the Trusted Platform Module (TPM), a hardware device embedded in servers. VMkernel modules that load onto disk and memory are digitally signed and validated during load to ensure the authenticity and integrity of dynamically loaded code and protect against malware attempting to modify VMkernel as it persists on disk. VMKernel also uses memory integrity techniques at load-time coupled with microprocessor capabilities to protect itself from common buffer-overflow attacks used to exploit running code.
Encryption: Ensure secure connection to VMware ESX and ESXi hosts with SSL encryption.
Enable authentication for iSCSI Devices: VMware ESX and ESXi secure iSCSI devices from unwanted intrusion by requiring that either the host or the iSCSI initiator be authenticated by the iSCSI device or target whenever the host attempts to access data on the target LUN.
Network Security Policies. Enforce security for virtual machines at the Ethernet layer. Disallow promiscuous mode sniffing of network traffic, MAC address changes and forged source MAC transmits.

Manageability

Several management interfaces are available to more efficiently manage VMware ESX and ESXi environments. The core management interfaces used by VMware ESX and ESXi administrators are:

VMware vSphere Client. Manage VMware ESX or ESXi hosts, virtual machines and (optionally) VMware vCenter Server with the common user interface of the VMware vSphere Client. The vSphere Client is available as a free download and can be pointed at a VMware ESX or ESXi host for single host management, or it can be pointed at VMware vCenter Server for multi-host management.
VMware vCenter Server. Enable centralized management for VMware ESX and ESXi hosts and their virtual machines. To manage an ESX or ESXi host with VMware vCenter Server, a VMware vCenter Agent license, included in all editions of VMware vSphere, is required for that host. VMware vSphere includes many more management capabilities that improve business continuity and maximize operational efficiency such as live migration, automatic load balancing, protection against hardware failures, and virtual machine back up and restore capabilities.

Additional management tools for VMware ESX and ESXi include:

VMware vSphere Command-Line Interface 4.0 (vCLI). Manage VMware ESX and ESXi through a remote execution environment. The latest version of vCLI has a number of new commands and is supported on both VMware ESX 4.0 and VMware ESXi 4.0.
VMware vSphere Power Command-Line Interface 4.0 (PowerCLI). Manage and configure thousands of Virtual Machines with this powerful yet easy to use interface that is based on Microsoft PowerShell technology. PowerCLI allows IT administrators to manage VMware ESX or ESXi through a scripting interface managing the same tasks done with the VMware vSphere Client.
VMware vSphere Management Assistant. The VMware vSphere Management Assistant is a virtual machine that includes a VMware vSphere command-line interface and other prepackaged software that developers and administrators can use to run agents and scripts to manage VMware ESX and ESXi hosts.
Agent-less Hardware Management with CIM. Common Information Model (CIM) provides a protocol for monitoring hardware health and status through VMware vCenter Server or CIM-compatible third-party tools.

*The free version of ESXi is limited to 4-way virtual SMP.

VMware ESXi FAQs:

Why is VMware making ESXi free?

VMware is making its standalone ESXi hypervisor available at no cost in order to help companies of all sizes experience the benefits of virtualization. Customers have shown tremendous interest in ESXi due to its innovative architecture, simple setup, and high performance. Allowing IT administrators to obtain VMware ESXi for free enables everyone to gain access to VMware's datacenter technology and prove its value in their own companies.

Can I get support for VMware ESXi?

Customers who use the free VMware ESXi product have several support options.

Can I run virtual machines created by Microsoft Virtual Server, Microsoft Virtual PC, or VMware Server on VMware ESXi?

Yes. You can use the free VMware vCenter Converter to import virtual machines that were created using VMware Server, Microsoft Virtual Server, or Microsoft Virtual PC version 7 or higher. VMware vCenter Converter also supports conversions from sources such as physical machines and certain 3rd party disk image formats.

What tools can I use to manage my free VMware ESXi license?

VMware recommends using VMware vSphere Client to manage VMware ESXi. You may also query the VMware ESXi host with the vSphere Command-Line Interface 4.0 (vCLI). Note that the free version of VMware ESXi does not allow any configuration changes for the VMware ESXi host through the vCLI. Further, managing a VMware ESXi host with VMware vCenter Server requires a VMware vCenter Server Agent license for each host, which is included in all editions of VMware vSphere.

What is the difference between VMware ESX and VMware ESXi?

VMware ESX and VMware ESXi are both bare-metal hypervisors that install directly on the server hardware. Both provide industry-leading performance and scalability; the difference resides in the architecture and the operational management of VMware ESXi. Although neither hypervisor relies on an OS for resource management, VMware ESX relies on a Linux operating system, called the service console, to perform two management functions: executing scripts and installing third party agents for hardware monitoring, backup or systems management. The service console has been removed from ESXi, drastically reducing the hypervisor footprint and completing the ongoing trend of migrating management functionality from the local command line interface to remote management tools. The smaller code base of ESXi represents a smaller “attack surface” and less code to patch, improving reliability and security. The functionally of the service console is replaced by remote command line interfaces and adherence to system management standards.

How is VMware ESXi different than VMware vSphere?

VMware ESXi is a hypervisor that partitions a physical server into multiple virtual machines. VMware vSphere is the industry’s first cloud operating system that drastically reduces ongoing costs and increases control over delivery of service levels while still preserving the flexibility to choose between any type of OS, application and hardware architecture. VMware vSphere offers organizations high availability and centralized management functionality that span across multiple ESXi hosts such as live migration, protection against hardware failures, power management, and automatic load balancing. VMware vSphere relies on a hypervisor to partition servers. Customers can choose to deploy either VMware ESX or VMware ESXi as part of the VMware vSphere suite. All the functionality of VMware vSphere is supported on both VMware ESX and VMware ESXi. In fact, VMware vSphere supports server resource pools that contain both hypervisors.

How do I use VMware vCenter Server to manage my VMware ESXi hosts?

VMware vCenter Server provides centralized management for ESXi hosts and their virtual machines. To manage an ESXi host with vCenter Server, you must have a vCenter Server Agent license, which is included in all editions of VMware vSphere.

What is the difference between VMware ESXi and VMware Server?

VMware ESXi is an enterprise-class hypervisor that offers a bare-metal architecture for near-native performance, features like memory de-duplication to increase consolidation ratios and a cluster file system for managing VM files on shared storage. VMware ESXi and VMware ESX are the critical foundations for a dynamic and flexible virtual infrastructure.

VMware Server installs as an application on Windows or Linux, relying on the operating system for resource management. This limits the performance and scalability. VMware Server is popular for test and development activities. Virtual machines created using VMware Server can run on VMware ESXi, but they must first be converted using the free VMware Converter.

Can I buy VMware ESXi preinstalled on servers?

VMware ESXi is the industry's first hardware-integrated hypervisor. Dell, IBM, HP and Fujitsu-Siemens have already started shipping server units with ESXi embedded. Several other OEMs such as NEC and Fujitsu have announced that they will soon start shipping servers with ESXi. View the hardware compatibility web page for a full list of the server models that have VMware ESXi preinstalled.

What are the Hardware requirements for ESXi?

The standalone version of VMware ESXi is certified on hardware listed in the hardware compatibility list (HCL). This list will continue to expand as we certify more servers to run ESXi. Review the ESXi Setup Guide for minimum hardware requirements.

What Operating Systems can I run on ESXi?

VMware offers the broadest operating system support as compared to any other virtualization vendor.

Will VMware Update Manager Patch my ESXi hosts?

VMware Update Manager will update both VMware ESX and VMware ESXi. An update utility is also provided for environments where VMware Update Manager is not present.

Note: The VMware ESXi host must be licensed for VMware vSphere to patch the host using VMware vCenter Update Manager.

Are there any VMware ESX features that are not compatible with ESXi?

Some specific networking features are not available in VMware ESXi, primarily those requiring configuration through the Service Console.

Is it possible to download a virtual appliance into an ESXi environment for evaluation?

Yes. If you are running VMware vSphere Client 2.5 and later along with ESXi 3.5 or ESX 3.5 or later, it is possible to access a list of downloadable virtual appliances for evaluation into an ESXi environment. To access that list of virtual appliances, open your VMware vSphere client, select "Virtual Appliance" from the file menu, and then select "Import...". When you select “Import from the VMware Virtual Appliance Marketplace” and click “Next”, you will be sent to a page where you can download the appliances.

Comparison on the Essential Functionalities of a Hypervisor:

The hypervisor is a critical component of and foundation for a virtual infrastructure. VMware was the first to bring a bare-metal hypervisor to market back in 2001 and since then has continued perfecting it by adding features in response to ever-increasing customer needs. Today, as virtualization becomes ubiquitous, companies both small and large, are looking beyond simple server consolidation as a reason to adopt virtualization. Fundamental characteristics of a hypervisor are:

Have a purpose-built, thin OS independent architecture for enhanced reliability and robustness
Make optimal use of available hardware resources
Deliver performance acceleration features that support mission critical applications
Enable advanced capabilities not previously possible on physical systems

Ten of thousands of companies have already adopted VMware ESX/ESXi making it the most proven foundation of today’s virtual infrastructure. Its reliability was rated by industry press as "virtually bomb-proof" (Redmond Magazine, 2008 Editor Choice Award). VMware ESX/ESXi is the only hypervisor in the market that can truly provide the essential capabilities to satisfy today’s customer requirements.

The following table compares VMware ESX/ESXi 3.5 with the recently released Microsoft Hyper-V hypervisor and shows how Hyper-V presents substantial limitations in all critical aspects of a hypervisor:

Thin and Purpose-Built Architecture
Features	VMware ESX/ESXi 3.5	Microsoft Hyper-V RTM	Hypervisors Comparison
Small disk footprint			Hyper-V is fully dependent on a general-purpose OS(Windows 2008). Microsoft’s best-case disk footprint is 2.6GB (Hyper-V + Server Core), which is more than 80x times larger than ESXi's (32MB). Hyper-V + Windows Server 2008 is even larger with a footprint of ~10GB. The large size of both options creates an easier target for security attacks and increasing performance overhead. Also, patches to Windows Server 2008 / Server Core will affect Hyper-V guests. VMware ESXi on the other hand is a fully functional hypervisor in a 32MB disk footprint, which reduces the risk of downtime and increases reliability.
OS independence			Hyper-V depends on Windows 2008 and is consequently biased towards Windows guests when it comes to making full use of the available hardware resources: Hyper-V support for non-Windows guest OSs is limited to only Novell SUSE Hyper-V support for 4-ways vSMP is limited to Windows Server 2008. For Windows 2003, Hyper-V only supports up to 2-way vSMP VMware ESX/ESXi is optimized for virtualization, offers the broadest OS support (10 Windows versions, 16 Linux versions, 2 Novell Netware versions and 2 Sun Solaris versions) and allows all supported guest OSs to optimally utilize available resources (4-way vSMP is available on all supported server OSs)
Hardened drivers			Windows 2008 is a general purpose OS that relies on generic device drivers built by third parties that are not designed for virtualization. This fact dramatically increases the likelihood of performance problems, downtime related to driver patches, and system failures, even though the drivers go through Microsoft’s certification process. Windows drivers already go through Microsoft certification today and driver problems still exist. On the other hand, VMware works closely with IHVs to test and optimize their drivers for use with ESX/ESXi to ensure, overall reliability and performance when running concurrent virtualized workloads.
Resource Efficiency
Advanced memory management			System memory management is in most cases the dominant factor that determines the number of concurrent VMs that can run on a physical host. Hyper-V cannot overcommit host memory because it does not support features such as transparent memory page sharing and memory ballooning to reclaim idle physical memory. Consequently Hyper-V delivers lower virtual machine density, and low ratios of server consolidation compared to VMware ESX/ESXi. VMware ESX/ESXi fully supports memory overcommit, enabling high rates of VM density while delivering consistent performance. VMware customers regularly use memory overcommit in their production datacenters at rates of 1.5X to 2.5X without any noticeable impact to end-users.
Advanced storage management			Hyper-V uses the NTFS file system for storage. NTFS is not a clustered file system. Therefore, Hyper-V does not provide native support for shared virtual disks and live migration. Hyper-V’s lack of a clustered file system means that with Microsoft quick migration (based on host clustering) all VMs on a LUN will be migrated at the same time. To avoid this unwanted result, a user must assign one VM per LUN, which creates a storage nightmare. The only other option is to purchase a third party clustered file system at additional licensing and support cost. VMware ESX/ESXi comes with VMFS, a clustered file system designed specifically for virtualization. VMFS fully supports live migration, and enables multiple VMs to share a single LUN and still migrate/failover individual VMs.
Advanced networking management			Hyper-V does not support native physical NIC teaming, instead requiring 3rd party drivers from IHVs (Intel, Broadcom). This limitation prevents Hyper-V from providing out-of-the-box, hardware independent protection from NIC failure. Additionally, Hyper-V drivers for supported NICs are not virtualization aware, cannot be controlled from within the hypervisor, and must be loaded in the parent partition. VMware ESX/ESXi fully supports NIC teaming, resulting in a simple, comprehensive out of the box solution for NIC failover.
Performance Acceleration
I/O scalability			Hyper-V uses an “indirect driver” model that keeps all device drivers in a Windows 2008 instance running in the Parent Partition of Hyper-V and relies on the general purpose OS to handle the I/O traffic. In Hyper-V's model, all I/O requests from guest OSs must travel through Windows Server 2008 (or Server Core). This design negatively affects the efficiency of the process scheduler to manage I/O requests and results in higher latency. This impact is even more accentuated with virtual SMP as the number of processes handled by the scheduler must manage grows. The outcome is scalability issues when running many concurrent virtual machines under load, resulting in low consolidation ratios. VMware ESX/ESXi utilizes a direct driver model with a scheduler built specifically to handle the demands of multiple, high workloads. This scalability results in higher VM density ratios with while delivering consistent, high performance.
Distributed resource allocation			Hyper-V lacks many capabilities to optimally distribute hardware resources., based on real time workload conditions. Unlike ESX/ESXi, Hyper-V does not support: Network traffic shaping for load balancing Storage I/O prioritization to ensures that critical VMs receive priority access to storage devices Memory swap prioritization (memory ballooning) VMware ESX/ESXi has a proven solution for hardware resource distribution, including full support for network traffic shaping, I/O prioritization, and memory ballooning for memory management and prioritization.
Support for performance enhancing technologies			Hyper-V lacks support of several performance enhancing technologies such as: AMD RVI (nested page tables), included in the latest release of the AMD Barcelona CPU Large memory pages, which allows improved performance when virtualizing databases VMware ESX/ESXi supports both nested page tables and large memory pages and is therefore capable of superior performance even in the most demanding environments. Mission critical and intensive applications such as an Oracle database will perform better in a VMware virtual environment.
Linux paravirtualization support			Hyper-V supports the “old way” of doing Linux para-virtualization, where IT admins maintained two kernels, one for physical and one for virtual machines. This extra maintenance increased complexity and management costs. On the other hand, VMware ESX/ESXi supports Linux para-virtualization through paravirt_ops / VMI (Virtual Machine Interface) – the new industry accepted way to para-virtualize Linux. This new way does not require IT admins to maintain and support separate kernels for physical and virtual machines – it’s all in one kernel. Currently, SLES 10, and Ubuntu 7 and 8 all support paravirt-ops/VMI.
Advanced Virtualization Features
Virtual security technology			Hyper-V does not provide dedicated capabilities for security vendors to extend their security capabilities to virtualized environments. VMsafe, an upcoming feature of VMware ESX/ESXi, will enable a rich ecosystem of third-party security solutions for virtualized environments. VMsafe is a virtual security technology that provides fine-grained visibility over virtual machine resources, making it possible to monitor every aspect of system execution and stop previously undetectable viruses, rootkits and malware before they can infect a system.

Documentation:

VMware ESXi Data Sheet (.PDF)