It seems to take forever to defrag a hard drive sometimes. If I’ve got a heavily fragmented drive that is filled to 49% capacity, will it take significantly more time to defrag than to simply copy half the disk? If so, what is all the extra work it’s doing? Seeking sectors? Verifying the copy?
That’s difficult to answer, because it depends on a lot of factors.
It depends on how fragmented the disk is, the size of the fragmented files, how far-away the fragments making up each individual file are from each other, how much of free space is available closer to the Partition Boot Sector, the location and size of immovable system files and paging/swap files, and the tool being used to perform the defragmentation (each tool uses its own algorithms, which may differ greatly). The Windows native defrag tool takes an insane amount of time, but a lot of 3rd party tools work much faster and more efficiently.
Keep in mind that defragging involves constant moving around of data and the calculations required are far more intensive than a copy command. Add to that the fact that while the defragmentation is taking place, the OS is usually still actively reading/writing from/to the hard disk.
So, while defragmentation is more processor intensive than copying, it doesn’t need to move large paging and swap files, whereas your simply copy half the disk scenario would need to read and write these files.
I use (and recommend) the freeware version of the Diskeeper defrag software:
If you prefer to spend money, try Ashampoo Magic Defrag: