so, what is the issue exactly? how are you missing 48GB?
if you have a eg 500gb hard drive, and you have gone into windows or any operating system to check how much you have and it says 452GB this is normal, nothing you can do about it.
it's because of the way operating systems read 1GB, manufacturers will put 1000mb for 1GB and windows will read 1024mb for 1GB. so when you check you will not see 500GB but less, this is normal, and it doesnt mean you dont have 500gb.
also depending on the format, there are hidden files and tables that are used on the drive that also take up space, aswell as things like system restore that will have hidden backups on drives.