Virtualization is normally used to provide workload consolidation, but this means, without the right resource management, just blending everything together; this could become a risk, like putting all your eggs in one basket without taking any precautions. In addition, all shared components of your infrastructure will most likely be affected in some way by this big change (for example, the storage or the network). Moreover, standard procedures such as monitoring, backups, patching, and administration will be also affected.
As a good practice, before virtualizing an existing environment, you need to assess all parts of your infrastructure not just the servers you plan to virtualize to uncover any potential problems or hurdles that may impact your project. The old woodworking rule measure twice, cut once also applies to information technology; be sure to get accurate measurements to drive the right project in the right way.
Of course, be sure to have a healthy environment before attempting to virtualize it, just to avoid incorrect measures, such as workloads with existing performance or application issues, to avoid the risk of just moving those issues to the virtual environment. Depending on the data that you collect, your conceptual and logical design (as described in the previous chapter) may remain the same, but the physical design should take account of real and objective data to be sure of a successful project. The existing environment could be physical, as was typical in the past, or mixed with some physical and virtual workloads, or already fully virtualized.
Most virtualization projects will involve migrating your current physical servers to virtual machines using a physical to virtual (P2V) conversion, or even better using an application/service migration to a new virtual environment. Therefore, it is important that you thoroughly understand your current environment before attempting to move it to a virtual environment. By doing this, you can ensure that you purchase properly sized server hardware for the hosts and define the correct storage, both for the capacity and the performance. For this purpose, you will need to collect some critical metrics, as discussed in the next section.
However, it's not always the technical aspects; you need to consider the licensing impact, not only for the virtual environment (for example, more hosts, more VMware licenses) but also for applications and services and operating systems where you may need new or different licenses.
Also, it's important to identify whether the old physical hardware could be reused for the virtualization; for example, for disaster recovery, or for other purposes (such as physical domain controller servers or backup server roles). In this case, you have to consider both the technical possibilities (for example, does the server have enough resources?) and the practical and organizational possibilities (is the server still supported and how much does it consume and cost during operation compared to a new server?).