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The Market For Virtualization Is Growing An Osterman Research survey published in December 2009 found that for in-house email servers, a combination of physical and virtual servers is the preferred delivery model (76%). However, virtual servers are used across a wide and growing variety of other application server and application types.

Storage virtualization, for example, is growing in popularity because it helps an organization achieve much greater flexibility in content management by separating physical and logical storage. Using a Storage Area Network (SAN), for example, an organization can build out a storage network independently from the servers, client platforms and applications that create and access data. This can drive down the cost of storage and allow better performance of the overall network.


What Is Fragmentation? Disk fragmentation occurs when an operating system distributes pieces of a file in non-contiguous blocks on a hard disk platter. For example, when File A is originally saved to disk, it is saved in a contiguous block. File B is then created and saved in a contiguous block in the first available space after File A. When File A is opened at a later date and new content is added to it, the new information is stored in the next space available after File B. Over time and repeated open-save cycles, pieces of File A can be scattered all over a hard disk platter. Although fragmentation is a serious problem, it is actually a consequence of storage systems attempting to make the best use of available space.

While file fragmentation does not directly impact the integrity of content, it has a number of negative consequences, including:

  • Slower access to information

  • Greater I/O requirements that can impact

system performance

  • More wear-and-tear on disk drive hardware

  • More frequent hard disk and application crashes

The Benefits Of Defragmentation Defragmentation reverses the fragmentation process by redistrib- uting disk-based content into contiguous blocks of information. This results in much better disk drive and overall system perfor- mance because less work is required to access content, resulting in reduced I/O requirements. Defragmentation can also lead to longer disk drive life because the hardware undergoes less stress during read/write cycles.

Defragmentation is an important process for any server, client machine or other disk-based device—virtualized or not—since disk access times are orders of magnitude slower than memory access


times and, as such, are a major bottleneck in overall system performance. For example, fast, server-grade hard disk drives have access times of around two milliseconds. Static RAM, on the other hand, has access times of around 10-15 nanoseconds— roughly 130,000 to 200,000 times faster than a hard disk. Consequently, improving the performance of disk access through defragmentation will address one of the major bottlenecks in system performance.

Fragmentation Also Occurs In Virtualized Environments The need for defragmentation is even more acute in virtual environments. This is because physical hardware in a virtualized storage environment must support more operating systems and so can undergo even more disk access and more stress than in a non-virtualized environment. Further, disk I/O in one virtual machine has a cascading effect on disk I/O in other virtual machines, and so the problem of excessive disk I/O in virtual machines is, in fact, even worse than what would be experienced in a physical disk environment.

Virtual Environments Compound The Problem While fragmentation in a physical storage infrastructure can reduce system performance, fragmentation in a virtual storage infrastructure can be even worse. This is because virtual disks— many of which can be housed on a physical disk—can become fragmented over time just like the physical disk(s) on which they reside. The result is a fragmented virtual disk on a fragmented physical disk, or fragmentation within fragmentation. This results in even slower system performance than would be experienced in a physical storage infrastructure.

The Bottom Line: Virtualized Environments Need Defragmentation As Much Or More Than Physical Ones Virtualized storage environments need to be defragmented just like physical storage environments. This is not only Osterman Research’s or Diskeeper’s recommendation, but also that of leading virtualization vendors. For example:

  • VMware has stated, “for best disk performance…run a disk defragmentation utility inside the virtual machine.”

  • Similarly, Microsoft advises clients “defragment[ing] the physi- cal machine…is particularly helpful if you have dynamically expanding or differencing virtual hard disks because they tend to fragment quite a bit.”



2 http://social.technet.microsoft.com/Forums/en/winserverhyperv/thread/2ca1dff1- 5612-4571-9736-d62a80e86f8e

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