Datasheet

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EXPLORING VMWARE VSPHERE 4 11
Chapter 14, ‘‘Automating VMware vSphere,’’ provides more information on vCenter Orches-
trator and other automation technologies and tools.
VMware vSphere Compared to Hyper-V and XenServer
It’s not really possible to compare some virtualization solutions to other virtualization solutions
because they are fundamentally different in approach and purpose. Such is the case with VMware
ESX/ESXi and some of the other virtualization solutions on the market.
To make accurate comparisons between vSphere and other virtualization solutions, one must
include only type 1 (‘‘bare-metal’’) virtualization solutions. This would include ESX/ESXi, of course,
and Microsoft Hyper-V and Citrix XenServer. It would not include products such as VMware Server
or Microsoft Virtual Server, both of which are type 2 (‘‘hosted’’) virtualization products. Even within
the type 1 hypervisors, there are architectural differences that make direct comparisons difficult.
For example, both Microsoft Hyper-V and Citrix XenServer route all the virtual machine I/O through
the ‘‘parent partition’’ or ‘‘dom0.’’ This typically provides greater hardware compatibility with a
wider range of products. In the case of Hyper-V, for example, as soon as Windows Server 2008—the
general-purpose operating system running in the parent partition—supports a particular type of
hardware, then Hyper-V supports it also. Hyper-V ‘‘piggybacks’’ on Windows’ hardware drivers
and the I/O stack. The same can be said for XenServer, although its ‘‘dom0’’ runs Linux and not
Windows.
VMware ESX/ESXi, on the other hand, handles I/O within the hypervisor itself. This typically pro-
vides greater throughput and lower overhead at the expense of slightly more limited hardware com-
patibility. In order to add more hardware support or updated drivers, the hypervisor must be updated
because the I/O stack and device drivers are in the hypervisor.
This architectural difference is fundamental. Nowhere is this architectural difference more greatly
demonstrated than in ESXi, which has a very small footprint yet provides a full-featured virtu-
alization solution. Both Citrix XenServer and Microsoft Hyper-V require a full installation of a
general-purpose operating system (Windows Server 2008 for Hyper-V, Linux for XenServer) in the
parent partition/dom0 in order to operate.
In the end, each of the virtualization products has its own set of advantages and disadvantages, and
large organizations may end up using multiple products. For example, VMware vSphere might be
best suited in the large corpor ate datacenter, while Microsoft Hyper-V or Citrix XenServer might
be acceptable for test, development, or branch-office deployment. Organizations that don’t require
VMware vSphere’s advanced features like VMware DRS, VMware FT, or Storage VMotion may also
find that Microsoft Hyper-V or Citrix XenServer is a better fit for their needs.
As you can see, VMware vSphere offers some pretty powerful features that will change the
way you view the resources in your datacenter. Some of these features, though, might not be
applicable to all organizations, which is why VMware has crafted a flexible licensing scheme for
organizations of all sizes.