Best allocation unit size for external HDD

Question

What is the best allocation unit size for a 2 TB external hard drive?

It will be primarily used as a file storage. My main goal is to save space, and performance isn't a priority. No software will be installed, neither any torrent client will be connected to it. No partitioning will be done to it as well.

The drive will mostly contain:

• PDF files (with file size ranging from a few KB to 60 MB)
• Media files (50-800 MB)
• ISO images (3 GB, 8 GB, and 13 GB files)

Solution

I don't know which OS you are using but you are good to go with default allocation size provided by the OS at the time of format. As you mentioned that you have a lots of small size files in that case less allocation size is best to not let your space wasted. Just go with default and enjoy.