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I was now copying a folder which contains thousands of small files (about 3-4 KB each) from my laptop to my external hard disk. The whole folder should be around 40 MB. However, I noticed the process took quite long (about half an hour on USB 3.0).

So, I went to check the copied folder's size using Explorer (Windows 10 by the way), and to my surprise the folder properties shows "Size: 40 MB"; "Size on disk: 5 GB", as seen in the screenshot below.

Any explanation to why is this happening? Is this normal? By the way, my hard drive still has about 250 GB left, so it's not really running out of storage space, if this is of any relevance.

Edit: I do (kind of) know the difference between size and size on disk, just asking if it is normal for the difference between them to be this big (from 40 MB to 5 GB).

enter image description here

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    Does this answer your question? What is the difference between “Size” and “Size on disk?”
    – Robert K. Bell
    Commented Sep 21, 2020 at 0:27
  • @RobertK.Bell I kinda know the difference in theory, but can the difference be that large, from 40 MB to 5 GB?
    – Anis R.
    Commented Sep 21, 2020 at 0:32
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    What file system does drive D: use? If it is exFat what you are seeing is entirely possible. The default cluster sizes for exFat are very large for large volumes and very inefficient for small files.
    – LMiller7
    Commented Sep 21, 2020 at 1:17
  • @LMiller7 Thanks for the input! Indeed it is exFat, as I use the drive on both Windows and Mac OS. So, I guess this explains the large size on disk then. Any way to improve the efficiency though? Can the default cluster sizes be changed? Asking just for curiosity, it does not bother me much for now aside from copy times.
    – Anis R.
    Commented Sep 21, 2020 at 14:51
  • The space inefficiency is inherent in the large cluster size. The only way I know to change that would be to reformat the drive and that would be data destructive.
    – LMiller7
    Commented Sep 21, 2020 at 18:03

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