Tuesday, June 19, 2018

hard drive - Why is "size on disk" much bigger than "size" when I copy data from NTFS to exFAT?


I tried to backup from my NTFS external hard drive to a new exFAT external hard drive. When the copy finished I saw that I have very little free space remained. I checked my file size and I saw that the real size of my file is "30.4GB" but the size on disk is "396 GB".


I must mention that number of file is so high (about 96110 Files, 10807 Folders).


Why has this happened? How should I fix this? I formatted my new hard drive with exFAT filesystem with Allocation unit size of 4096 kilobytes.


Answer



If my calculations are right than average file size on your exFAT is 331,7KB, but you've set minimal unit size to 4096 KB, which means that there is 92% unused space in every unit, so 96110 (files) x 3768,32 (freespace) = 362173235,2 KB = 345,40 GB (free) + 30,4 (real) = 375,8 GB, still missing few gigs somewhere, maybe because of that average size.


In other words, set unit size as small as possible or use ".tar" or something like that.


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