The difference usually happens because you have a lot of small files, Consider this:
-
50,000 files
-
32 KB cluster size (allocation units), which is the max for FAT32
for each file averaged 2 KB, you’d get about 100 MB total – but you’re also wasting 15x that (30 KB per file) on average due to the allocation unit size.
Real file size will be 100mb
Actual size on disk will be 50000*32000 wasting 15x that (30 KB per file) on average due to the allocation unit size