Defragmenting cancels and ends up with higher fragmentation, how?

Blooker

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Dec 23, 2013
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I often defragment my PC's hard disks, just for the speed and convenience but as you may know the times that it takes can fall out higher so I cancel it sometimes.

However every time I cancel the process at as example the half (50% done), the new fragmentation after interrupting, will be 3 times higher than when I decided to defragment at all.

If someone knows how this happens, does it mean an huge performance decrease or data corruption or not? I hope that it doesnt affect anything but fragmentation (speed) until I defragment on a day I have time to let it finish.

Its like;

I'm going to analyze me disk, see fragmentation at 10% and start defragmenting
2 hours later: Oh, its still going and I need my PC, lets cancel it already now. Hmm, it's now like 25%... so I did more bad than good by starting this today, at all
 
Solution
The defragmenter has to move some files to a temporay location in order to make room for the defragmentation process. If you cancel the defrag, it just leaves those files where they sit, possibly making fragmentation worse. This shouldn't corrupt your files in any way.

Your best best is to let it run overnight as spdragoo said.

spdragoo

Expert
Ambassador
Depending on the PC & the version of Windows, it really shouldn't be taking hours upon hours to defragment a hard drive...which means either that it really needs defragmented, or there might be another issue going on.

The best short-term solution is, since it's apparently going to take some time, what you should do is wait until you're absolutely done with the PC for the day, & let it defrag overnight. Set it up right before going to bed, & (hopefully) by the next morning when you get up it'll be complete -- or at least have just a little bit of time left so that you can let it continue while you're at work/school/running errands.
 
The defragmenter has to move some files to a temporay location in order to make room for the defragmentation process. If you cancel the defrag, it just leaves those files where they sit, possibly making fragmentation worse. This shouldn't corrupt your files in any way.

Your best best is to let it run overnight as spdragoo said.
 
Solution

Blooker

Honorable
Dec 23, 2013
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10,520
Thanks for the explanations, I had no trouble with finding a timespace and it wasn't just about 1 PC, but I just wanted to know the technical mechanism causing the difference. Hawkeye you explained it very well, but.. Is it then only moved by low-level disk index? Because the actual file explorer locations won't change..