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.