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I want to defragment my external hard drive which is 500 GB in size. It's divided into two partitions of 232 GB each. One has 70.5 GB free, and the other has 42.5 GB free. Can I defragment it now or do I still have to delete some of the data?

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I'm wondering if this could take long(about 6 hours), considering the amount of file that is stored on the drive. – Ieyasu Sawada Apr 29 '11 at 4:59
You can always Cancel a defrag process if you feel it takes too long. – icelava Apr 29 '11 at 9:58
up vote 2 down vote accepted

I believe the Windows Disk Defragmenter requires around 15% free disk space to perform defragmentation. Third party software can work with a lower figure than this - for example, PerfectDisk 11 only needs as little as 1% free disk space to do its work.

In effect you need to have at least enough space to move around the largest file fragment on the disk. You should be good to defragment now without having to delete any more data.

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You should not need to delete any data. Diskeeper can defrag in low free space conditions as well as consolidate the free space.

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