Virtualization and Disk Performance

Short Description
Given that virtualization technologies have many specific applications this paper will begin by first presenting definitions.
Definition: Virtualization
Essentially to virtualize something means to make something that doesn’t actually (physically) exist appear to exist. Think of the context in virtual reality. Let’s make a quick example of something everyone in IT is familiar with, a PC with 4 logical volumes (C, D, E, and F). In reality that desktop has one physical disk drive partitioned into 4 volumes. A logical volume is in this case a virtual drive.

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Definition: Storage Virtualization
Storage virtualization involves the creation of a usually very large, logicalpool of data that, via software, appears to be physically located all on one server. In actuality, that data may be located across hundreds of physical disks spread across dozens of servers. This is the concept implemented by Storage Area Networks (SAN). For peak performance these storage pools require automatic disk defragmentation just the same as a single hard drive would. Automatic defragmentation is implemented from server(s) that manage the respective logical disk volumes.
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Virtualization does have its dangers, as it incurs greater stress on physical resources. While under utilization of CPU may be a driving factor to virtualize servers, other hardware resources may become overtaxed. Given that a host system has limited ability (depends on application) to page memory used by the guest systems, the most recognized bottleneck to address is physical memory (RAM). Options to programmatically alleviate memory bottlenecks incur performance issues when the disk is re-introduced. Another major component and perhaps less acknowledged is the disk subsystem. In many cases, depending the purpose and application of the guest/virtual systems, the disk bottleneck will be the most significant barrier to performance.
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