I just took delivery of a 5 terabyte external hard drive, to use as one of my off-site drives. The drive was formatted with exFAT.

This post isn't about backups at all, just some things I noticed when I went to prepare the drive for my use.

The first thing I noticed is that directories take up 256 kilobytes as soon as they are created. Files have a similar minimum allocation, so that a 33 byte file actually sits on 262144 bytes. If you have five terabytes to play with, that's no big deal, but still...

The result is that while df reports that the drive has 131M occupied, tarring the files with no compression results in a 19M tarball.

Clearly exFAT is designed for a fairly flat directory structure, with very large files.