Virtualization Strategies for the CIO
Selecting a virtualization hypervisor begins with an important choice: Do you need a hosted or bare-metal hypervisor? Once you decide which type of
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hypervisor you need, there are lots of factors to consider.
You want a virtualization hypervisor that’s compatible with your hardware, allows for simple management and gives you the performance your virtual infrastructure needs. You should also consider high availability, reliability and scalability. And of course, look into costs.
Here are eight considerations for choosing a virtualization hypervisor:
Performance
If you want high performance, a bare-metal virtualization hypervisor is really your only
option. Bare-metal virtualization offers the least amount of resource overhead. Bare-metal
virtualization hypervisors also have advanced resource controls that allow you to guarantee,
prioritize and limit virtual machine (VM) resource usage.
Hosted hypervisors typically have no or limited resource controls, so VMs have to fight each other for resources. Unlike bare-metal virtualization, hosted hypervisors often have steep resource-overhead penalties, especially when operating system services, tools and applications are running on the guest operating system.
Hardware compatibility
Hosted hypervisors tend to facilitate hardware compatibility because they run on Windows or
Linux, and you can almost always find a device driver for a host running those OSes. Some
bare-metal virtualization hypervisors, such as VMware ESX and ESXi, work with a limited set of
certified hardware. Microsoft Hyper-V does not have this restriction, however, because any driver
that works with Windows will work with Hyper-V.
Ease of use
Hosted virtualization hypervisors are also easy to install, use and maintain. Plus, they
typically do not require specialized skills. Most hosted hypervisors install like an application
and are fairly intuitive. Bare-metal virtualization hypervisors are fairly easy to install as well,
but they can be complicated to configure. With a bare-metal hypervisor, you really need to know
what you’re doing.
High availability
Bare-metal virtualization hypervisors offer high-availability
features, which provide continuous availability in the event of a host failure. VMware has numerous
availability features, including vMotion,
VMware High
Availability and Fault Tolerance. Microsoft Hyper-V has some limited, less-integrated options
for high availability, and Citrix Systems XenServer offers HA with certain licensing tiers and
through third-party products. Hosted virtualization hypervisors typically lack high-availability
features, so if a host fails, VMs are down until you resolve the problem.
Reliability
When it comes to reliability, bare-metal hypervisors definitely have an edge. This type of
virtualization hypervisor typically goes through more quality-assurance testing than hosted
products, because they’re aimed at data centers that don’t tolerate bugs and other issues.
Additionally, because there is no host OS running on a bare-metal hypervisor, that’s one less
component that can potentially fail.
Hardware drivers cause many failures in both hosted and bare-metal virtualization hypervisors. Hosted hypervisors use regular drivers that go through no special testing for virtualization. On the other hand, some bare-metal virtualization hypervisors, such as VMware ESX and ESXi, have a rigorous hardware certification process for all devices.
Virtualization hypervisor management
Bare-metal virtualization hypervisors have more options for management and automation. They
have centralized consoles that allow you to easily manage large numbers of hosts and VMs. Plus,
there are a huge number of third-party management and automation products for bare-metal
virtualization hypervisors. Hosted hypervisors, on the other hand, tend to be islands that admins
have to manage individually, which can be very tedious and time consuming in large
infrastructures.
Cost
When it comes to cost, hosted virtualization hypervisors have a big edge over bare-metal
hypervisors. Many hosted hypervisors are free or cost only hundreds of dollars. Bare-metal
hypervisors can be very costly, especially when you want to scale and use advanced features. Most
bare-metal virtualization hypervisors are advertised as free, but that’s only for the core
hypervisor. If you want to use advanced features or management tools, the cost can be many
thousands of dollars.
Scalability
If you want scalability, a bare-metal virtualization hypervisor is the only way to go. A
bare-metal hypervisor can scale very high, something VMware especially focused on in vSphere 5. In
vSphere 5, you can create single VMs with up to 1 TB of memory and 32 virtual CPUs, which should
satisfy any workload. With bare-metal hypervisors, you can easily run hundreds of VMs on a single
host if you have enough hardware resources.
In contrast, hosted hypervisors have very limited scalability, both in the size of the VMs and the number of VMs that can run on a single host. VMware’s hosted virtualization hypervisor, Workstation, can only support VMs with up to 32 GB of memory and 8 virtual CPUs.
This was first published in August 2011
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