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Do You Really Need A Defragmenter?

The short answer is yes.

A number of studies demonstrate that defragmenting a disk improves performance significantly. Despite that, some people argue strenuously that you don't need to defragment disks. There are two versions of this argument; both remain current because both of them have some basis in truth.

The unsophisticated version is, "I defragmented my disk and I didn't notice any improvement in performance. So why bother?"

While defragmentation has been shown to consistently improve disk performance by 50 or 100 percent or more, it's also true that disk access times are only a small part of overall computer performance. Even if you reduce the time to access a file by 50 or 100 percent, you may not notice the effect.

However, this argument is really the equivalent of "I didn't take out the trash this week, and no one noticed, so why bother?" Of course, if you never take out the trash, eventually you end up like the crazy old lady with 247 cats, newspapers stacked to the ceiling, and the Health Department knocking at the door.

"Fragmentation is a slowly erosive process," says Bob Nolan, CEO of Raxco, makers of PerfectDisk disk defragmenter. "It kind of nibbles away at you, and can be expensive in a stealth manner. Because it doesn't happen all at once, you tend not to notice."

Except of course, eventually you will notice. Often, fragmentation problems don't become really noticeable until the disk reaches a certain level of fragmentation. Then performance slows down radically. The other thing that can happen with a severely fragmented disk is that the system suddenly can't find a large enough chunk of space to install a new program, even though the disk shows that there's plenty of space left.

The more sophisticated argument is that, with modern disk controllers and storage architectures such as SANs in a multi-user environment, there's no gain from having the sectors of a file contiguous on the disk. As we noted, the disk controller makes the decisions about where to place file sectors on the physical disk. Since disk accesses are largely random in a multi-user system, and since the controller rather than the operating system determines where each cluster goes on the disk, the argument goes, why bother defragmenting the disk?

"That's absolutely right – and completely wrong," says Nolan. What the argument ignores, he says, is that if the disk is logically fragmented, the controller has to work much harder to retrieve it. While the disk heads don't have to go skating all over the platters chasing down the fragments, each logical fragment generates a separate seek command to the controller, complete with the starting address and the length of the fragments. If you have 100 logical fragments, every one has to be dealt with by the controller separately. "Which do you think is faster?" he asks. "Doing it 100 times or doing it once?"

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