Not all applications or server workloads are good candidates for virtualization. It is important that these workloads are identified early on in the design process.
There are a number of reasons why a server or application may not be suitable for virtualization. Some of these include the following:
- Vendor support
- Licensing issues
- Specialized hardware dependencies
- High resource demand
- Lack of knowledge or skillsets
A common reason to not virtualize an application or workload is the reluctance of a vendor to support their application in a virtual environment. As virtualization has become more common in the enterprise data center, this has become uncommon; but, there are still application vendors that will not support their products once virtualized.
Software and operating system licensing in a virtual environment can also be a challenge, especially when it comes to physical server to virtual machine conversions. Many physical servers are purchased with Original Equipment Manufacturer (OEM) licenses, and these licenses, in most cases, cannot be transferred to a virtual environment. Also, many licenses are tied to hardware-specific information, such as interface MAC addresses or drive signatures. Licensing issues can usually be overcome. Many times, the primary risk becomes the cost to upgrade or acquire new licensing. As with other potential design risks, it is important that any issues and potential impacts licensing may have on the design be identified early on in the design process.
Some applications may require the use of specialized hardware. Fax boards, serial ports, and security dongles are common examples. There are ways to provide solutions for many of these, but often, given the risks associated with the ability to support the application, or the loss of one or more of the potential benefits of virtualizing the application, the better solution may be to leave the application on dedicated physical hardware. Again, it is important that these types of applications be identified very early on in the design process.
Physical servers configured with a large amount of CPU and memory resources where applications are consuming a large amount of these resources may not be good candidates for virtualization. This also holds true for applications with high network utilization and large storage I/O requirements. vSphere 6.7 supports virtual machines configured with up to 128 virtual CPUs (vCPUs) and 6 TB of memory, but the high utilization of these configured resources can have a negative impact on other workloads in the virtual environment. These high-utilization workloads will also require more resources to be reserved for failover. The benefits of virtualizing resource-intensive applications must be weighed against the impact placed on the virtual environment. In some cases, it may be better to leave these applications on dedicated physical hardware.
Many administrators may lack knowledge of the benefits or skills to manage a virtualized data center. The administrator of a virtual environment must be well-versed with storage, networking, and virtualization in order to successfully configure, maintain, and monitor a virtual environment. Though this may not necessarily be a reason not to leverage the benefits of a virtualized environment, it can be a substantial risk to the acceptance of a design and the implementation. This is especially true with smaller IT departments, where the roles of the server, application, storage, and network administrators are combined.