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Granularity of Control and Hypervisor Communication Becoming the Prerequisites for Virtual Machine File System Defragmentation

2009 is shaping up as the year of server virtualization. The hype around Citrix XenServer, Microsoft Hyper-V and VMware ESX Server is giving way to the reality of companies actually virtualizing their production servers as a means to improve energy efficiencies and slash infrastructure costs. But as companies virtualize these servers, many are leaving the familiarity of direct attached storage (DAS) and entering the world of networked storage for the first time. This is creating new challenges, especially for Windows servers using utilities such as defragmenters that will begin to operate on virtual machines (VMs) and defragment each VM’s associated file system.

Defragmenting the file system associated with specific VMs takes on a larger challenge in virtualized server environments due to:

  • Performance impact. Whether running on dedicated physical machines or on VMs, defragmentation incurs a performance penalty of the host’s memory, CPU and storage when defragmentation runs on the host server. However the defragmentation’s performance hit is amplified on VMs since the resources of the underlying host physical server are shared among its guest operating systems.
  • Virtualization unaware. Most applications and operating systems are still not aware that they are virtualized and, as such, do not and cannot communicate with the underlying hypervisor. This becomes a problem when defragmenting the file systems associated with specific VMs since the defragmentation utility assumes that it is defragmenting a file system that resides on DAS and is not aware that the storage is under the management of the hypervisor and therefore needs to defragment this storage differently.

While vendors of defragmentation software are already aware of these problems in virtualized server environments, some defragmentation software is better suited to meeting these new challenges than others. For instance, Raxco Software’s PerfectDisk has two features that set it apart from competitors.

First, PerfectDisk distinguishes itself by defragmenting files and file system free space. Other defragmentation tools primarily defragement files which improves performance for existing files but if free file system space is not also defragmented, as new files are stored to the available space, the file system may have to fragment them as soon as they are stored. PerfectDisk prevents this problem by defragmenting the file system free space so as new files are stored, there is a greater likelihood that files will remain whole and not stored initially in a fragmented state.

The benefit that companies gain as physical machines running PerfectDisk are virtualized is that the performance impact when the defragmentation process runs is diminished. Since PerfectDisk defragments free file system space, new files are stored in a contiguous state so there are fewer files to defragment when PerfectDisk does execute. As a result, PerfectDisk executes in a shorter amount of time while decreasing the impact on the underlying physical server.

However not every company has the luxury of defragmenting the file system across an entire VM. If there are hundreds, thousands or even millions of files associated with a specific VM but only a few files that require defragmentation in order to improve application performance, it does not make sense to defragment the entire file system yet this is the way that defragmentation software often works.

This is the second way PerfectDisk sets itself apart from competitors. PerfectDisk provides administrators a list of the most fragmented files so they can configure PerfectDisk to defragment as few or as many of these files as they want. Again, this helps in virtualized server environments since the overhead associated with defragmenting just a few files is substantially less than defragmenting an entire file system.

This option becomes important in virtualized server environments since companies do not have to guess when the defragmentation of that specific file is complete. Using defragmentation software that does not have this option provides no insight into what files it has defragmented, it only reports on the progress that it has made on the file system as a whole. As a result, using competitive products administrators are only assured a file is defragmented when the entire defragmentation process is complete. Conversely using PerfectDisk in a virtual server environment, administrators have a better sense of what files are fragmented and be more selective when they run the defragmentation process so it does not bog down the entire VM or the underlying physical server.

Server virtualization is poised to rapidly change the corporate IT landscape in 2009 and, as it does, companies need to prepare for the unintended consequences that virtualizing physical servers will have on their day-to-day operations. Products like PerfectDisk illustrate that granularity of control will become ever more important in this new virtual world because the consequences of letting processes running unchecked are no longer acceptable or tolerable in this new world. But PerfectDisk, like most products, now needs to evolve to better communicate with the underlying virtual infrastructure to deliver the new range of benefits that most companies expect to realize from their virtual infrastructure in the coming years.


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