How to fill FAT32 file system(linux) easily? My device drive is 32GB, in which 5 GB space will be taken for OS

I'm using 32GB device(linux based), which is using FAT32 filesystem, i want to test one thing that what would be the device behavior when i fill the device space with some random files. normally side loading the contents will take more than a day to fill the device. it would be better to create junk files via shell script to fill the empty space. can anyone help me in this? I don't want use the below commands. In my case i want create actual files. fallocate -l 50G big_file truncate -s 50G big_file dd of=bigfile bs=1 seek=50G count=0