My name is Philipp C. Heckel and I write about nerdy things.

Server Virtualization with VMware Infrastructure (vSphere)

Distributed Systems, Virtualization

Server Virtualization with VMware Infrastructure (vSphere)


Download as PDF: This article is a slightly shortened version of my seminar paper. Feel free to download the original PDF version, or the presentation slides.

4. The Downside of Virtualization

Vendors of virtualization solutions often praise their software and make companies believe that a virtualized infrastructure reduces their expenses immediately. And in fact, virtualization certainly can reduce costs in various fields. But without considering all potential problems beforehand, it can turn to a losing deal very quickly. To make sure that this does not happen, both technical and business analysis are a necessity.

4.1. Technical Limitations

From a company’s point of view, the major problem of the currently available virtualization solutions is probably that they are not compatible to each other at all. Citrix, Microsoft and VMware merchandise their own products each with its own proprietary system without having to meet any standards. Having to choose between these products, companies have to bind themselves to one particular vendor for a long period of time. After they have chosen a solution, it is not possible to switch to another vendor’s product even if it would match better to the current business needs. For big data centers, this incompatibility could have enormous consequences and makes the analysis of what-if scenarios exceptionally important. Not only are there incompatibilities between the different vendors’ software, but also within each specific product many compatibility issues occur. The for an automated data center essential process of live migration only works if many qualifications are fulfilled. It is for instance not possible to migrate a virtual machine from a host with an AMD processor to an Intel based machine. Differences in the architecture and the feature set of both vendors make a live migration in most cases impossible (Creeger, 2008). In fact, the different instruction sets such as x86, i64 or PowerPC are a general problem. Once a company has decided which architecture to use in its data center, it is in most cases also bound to the virtualization software. VMware for instance only supports the x86, whereas Xen also supports PowerPC. Hence a heterogeneous IT infrastructure with different architectures or even different CPU manufacturers is almost impossible to manage or maintain.

Another important point is the performance of virtual machines. Due to the memory footprint of the hypervisor, the virtual machines on the host have less available memory for their own tasks. Furthermore, emulating and mapping every access to the CPU and RAM produces a significant administrative overhead. This reduces the overall performance of a host and therefore the performance of each VM. In comparison to the execution of an operating system on bare hardware, a VM does not perform “good or even fair” (Wolf et al., 2005).

4.2. Business Aspects and Costs

While companies are usually aware of the technical challenges, they often underestimate the monetary impact of a new IT infrastructure on their business.

Due to the fact that most data centers have grown throughout their lifetime, they do not consist of homogeneous servers. This makes live migration complicated or even impossible and can be difficult in terms of compatibility as well. The cost-intensive consequence of this is that incompatible hardware has to be replaced by new servers. Furthermore, since virtualization requires shared network storage devices such as Fibre channel or iSCSI, new storage and network devices have to be acquired and installed. Not only are they very expensive to buy, but they also eat up an enormous amount of power and form a big percentage of the overall data center cost.

Another often unconsidered aspect of an infrastructural change is the fact that even though the amount of servers reduces, the complexity of the data center increases. That is, administration gets more difficult and trained specialists will be necessary to supervise the new virtualized data center. Due to the fact that the number of operating systems in the new environment stays the same or even increases, the amount of required system administrators does not change significantly. It is even possible that more staff needs to be hired because the number of administrators “grows linearly with the number of VMs” (Creeger, 2008).

Virtualization makes it very easy to provide services like Web or FTP servers. Instead of having to set up a new machine, installing an OS and configuring the service, a VM can just be cloned from an existing machine or template. This can create a huge problem in terms of licensing costs if many virtual machines use non-free operating systems or software such as Microsoft Windows, IIS or SAP. Currently, most software vendors do not make any difference between a virtual machine and a physical computer. Without a sophisticated inventory management of soft- and virtual hardware, licensing costs could lower the expected savings and the return on investment.

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