SOURCE: Bruce Boyers Marketing Services

June 23, 2009 17:29 ET

Virtual Systems Fragmentation: Yes, It's Really There

BURBANK, CA--(Marketwire - June 23, 2009) - There are times when a system administrator or IT personnel might wonder if fragmentation is really a problem on virtual servers, such as those used in a SAN environment. It can really be a question of, "If I can't see it, is it really there?" A virtual system is not actually communicating to a directly attached disk, but instead is working on a virtual construct of a disk that is really a large file which may or may not be defragmented. This surface examination might lead one to believe that fragmentation isn't actually an issue with virtualization.

A closer look at how virtual systems operate and, more importantly, how they save and retrieve files, dispels this myth and reveals the fact that indeed fragmentation is present in virtual systems and has a major impact on performance.

Since a virtual machine has its own I/O request which is relayed to the host system, multiple I/O requests are occurring for each file request -- minimally, one request for the guest system, then another for the host system. When files are split into hundreds or thousands of fragments (not at all uncommon) it means the generation of multiple I/O requests for each fragment of every file. This action is multiplied by the number of virtual machines resident on any host server, and doing the math it can be readily seen that the result is seriously degraded performance.

But beyond that, each virtual machine operates its own instance of the Windows NTFS file system, and it has its own fragmentation quite in addition to that of the host. Even if the physical hard drive is relatively defragmented, the multiple virtual machines will have their own fragmentation -- it's literally "fragmentation on top of fragmentation." With the many virtual machines operating from a single drive or set of drives, performance can come to a complete standstill.

The only method of ensuring the smooth operation of virtual machines is with the right defrag technology. An automatic defrag solution ensures that files stored both at the hardware layer and at the virtual layer as well are consistently defragmented -- fragmentation is never an issue at all. Only otherwise-idle resources are used to defragment; users are never negatively affected by the defrag process, and scheduling is never required. Virtual machine performance and reliability are constantly maximized.

So although file fragmentation might not be readily "seen" in virtual environments, it is certainly there, and can certainly be felt when performance slows to a crawl. The right defrag solution will guarantee that this will never happen.

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