windows - Disk Defrag slowing computer down?

  • Lynda

    I asked How to speed up my computer? in another post and one answer was to run disk defrag. I have done this before and in the majority of cases (with multiple computers not just one) it seems to actually slow the computer down vs speeding the computer up. Why is this and what is going on?

    Note: I am referring to after the disk defrag is complete. Not while it is running.

  • Answers
  • Keltari

    Every time I hear, "You should defrag your disk!" I roll my eyes and chuckle a bit.

    There is absolutely nothing wrong with defragmenting your hard drive. Defragmenting reorders the data on the hard drive so that it is contiguous. "They say" that you will see a noticeable difference in speed, specifically faster. This was more true in the past, than it is now. Modern OSs, drives, and file systems benefit little from defragmentation. Yes, there are some cases where it makes a noticeable difference, but those are rare. Those occur on heavily used file systems where there are lots of writes/deletes going on. However, that is not the typical home or office user. A whole industry has popped up around defragmentation, and I personally feel its mostly snake oil. There are some benefits from advanced defragmenters, like moving data to the innermost track, etc. However, pure defragmention really provides little or no noticeable improvement.

    Now as for your computers slowing down after a completed defrag... I honestly believe its not true. I think you are consciously looking for a difference in speed (which probably didnt happen) and therefore, subconsciously you think its slower.

  • Related Question

    windows - Is defragging relevant to improving disk performance anymore?
  • Imran

    Does it stil make much difference, now that we have much faster and larger HDDs? Generally I find if disk performance is getting too slow, it's probably because of too little free space, and the solution is to buy a new HDD.

  • Related Answers
  • Dan Walker

    It is still relevant, but since the release of Vista, Windows has automatically defragged your hard drive when the computer was sitting idle. If you leave your computer idle for long periods, this is no longer something which must be done manually.

  • Arjan

    It's not relevant on SSDs, which are hardly (if at all) affected by defragmentation (no read-heads to be moved around). And even more: SSDs have a much more limited number of times each part of the "disk" can be written to ("write endurance"; What is the lifespan of an SSD drive?), so especially for cheap SSDs it's best to use the whole disk, rather than keep using the same parts over and over again by running defragmentation tools.

    For those who've partitioned their hard drive: didn't that introduce a huge fragmentation?

    And though the question is tagged "windows", for those who get here given the generic title: it is not relevant for each file system. Like for a Mac (emphasis mine):

    You probably won't need to optimize at all if you use Mac OS X. Here's why:

    • Hard disk capacity is generally much greater now than a few years ago. With more free space available, the file system doesn't need to fill up every "nook and cranny." Mac OS Extended formatting (HFS Plus) avoids reusing space from deleted files as much as possible, to avoid prematurely filling small areas of recently-freed space.

    • Mac OS X 10.2 and later includes delayed allocation for Mac OS X Extended-formatted volumes. This allows a number of small allocations to be combined into a single large allocation in one area of the disk.

    • Fragmentation was often caused by continually appending data to existing files, especially with resource forks. With faster hard drives and better caching, as well as the new application packaging format, many applications simply rewrite the entire file each time. Mac OS X 10.3 Panther can also automatically defragment such slow-growing files. This process is sometimes known as "Hot-File-Adaptive-Clustering."

    • Aggressive read-ahead and write-behind caching means that minor fragmentation has less effect on perceived system performance.


    There is also a chance that one of the files placed in the "hot band" for rapid reads during system startup might be moved during defragmentation, which would decrease performance.

    Of course, the latter would not occur when using a Defrag utility that is included with the operating system.

  • zildjohn01


    On my friend's PC (XP, NTFS, 80GB HD, ~750MB free), the 700MB pagefile was in 11,000 fragments, and the MFT was in 40 fragments. I cleaned up the hard drive, defragmented, and rebooted, and the difference was very noticeable.

  • µBio

    It matters, but in Vista and Win7, it should be happening automatically as long as your machine has idle time.

    Lots of good info.

  • Mercer Traieste

    The speed brought by defrag is especially visible on slower hdds, like those on laptops.

  • Avery Payne

    I think it's still relevant. I have a C2Duo/2Gb/250Gbx2 setup, and even with the mirrored "small" drives, defragging seems to help tremendously with startup and program load times.

  • Chuck

    I would say it still makes sense - specially on hard drives that get a lot of file activities. I run MyDefrag at work to keep my hard drive from getting too fragmented, since at work I usually work on several revision depots that can have thousands of file changes in one day - keeping it defragged really helps on open read performance of the bigger art files I work with, but also on the speed of my text searches.