What is Fragmentation?

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Differentiating OS-level from application-level fragmentation

Disk fragmentation occurs when files are broken into hundreds or even thousands of pieces and scattered across your hard drive. This occurs naturally whenever files get created, deleted, or extended and even when the operating system is first installed. Even if you have plenty of free space, Windows still fragments files and before you know it, your once fast system starts to slow down. Microsoft recognizes fragmentation as a problem and recommends defragmenting your drives regularly.

File fragmentation causes a huge degradation in system performance, and over time can bring your system to a near crawl. Fragmentation causes your computer to use excessive resources (memory and CPU time) to complete tasks related to reading and writing files. This unnecessarily increases the work your computer must do to support the applications you are running. In cases of severe fragmentation, some applications may not run at all. Backup is one of the few operations that may actually read an entire disk. As disks grow in size, the time taken by the system to perform a full backup increases proportionally.

Fragmentation can cause applications to launch more slowly, file access to take longer, system boot/shutdown to slow, slow system hibernation/resume from hibernation, causes videos to drop frames and music to skip.

Fragmentation slows down your virtual environments as the virtual hard drive on the Windows host becomes fragmented and the Windows guest file system fragments.

Differentiating OS-level from application-level fragmentation

Unless you have experience maintaining a variety of computers comprising dozens of services, you may not realize all the areas where fragmentation can occur. When most people talk about fragmentation they mean specifically the hard disk, because that’s where slow performance is most noticeable. However, in even a simple computing environment, fragmentation occurs at the network level to the applications and services accessed both locally and remotely.

PerfectDisk has specific product lines catering to some of these areas, such as PerfectDisk 12 for Exchange, PerfectDisk 12 for VMWare, or PerfectDisk 12 Virtual Enterprise Edition. Microsoft Exchange Server has its own file defragmentation and compaction utility that PerfectDisk leverages. VMware and other virtual environments such as Hyper-V, Virtual PC, Virtual Server, and other such products also experience fragmentation for both host and guest machines, which PerfectDisk can handle for most Windows-based platforms. If you run SQL Server then you may know about its internal defragmentation, but what you might not know is that SQL cannot reliably report such information.

Microsoft offers a detailed explanation describing SQL Server’s internal defragmentation, which boils down to this: SQL Server is ignorant of how the operating system physically arranges its parts—and for good reason. Accordingly, SQL Server is unable to accurately report file fragmentation even when its on-disk parts are 100% fragmented. However, even when you defragment the SQL Server database it can still be fragmented in other ways. Read Microsoft’s explanation (linked above) for more detail.

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