The FAT32 filesystem is the closest thing we have to a universal standard for passing data around, but with the capacity of modern USB flash drives its 4 GB file size limitation has become problematic. exFAT is a popular contender for dealing with that, but the patent issues that surround it make true portability a pipe dream at best.

Enter UDF. As the filesystem of choice for DVDs and Blu-Ray disks, UDF support is ubiquitous. Appropriately-formatted disks are readable by operating systems dating back to the early 2000s. All that remains is figuring out how to format it. In general, there seem to be three important things to keep in mind:

  1. Remove all traces of previous filesystems. Different operating systems use different methods to detect what filesystems a disk contains, so ensure maximum reliability by eliminating potential sources of confusion.
  2. Format the entire disk, not just a partition. OS X seems to only look for UDF when the filesystem takes up the whole disk, as it does on DVDs, so overwrite the partition table before formatting the disk.
  3. Use the correct UDF version. UDF has a number of versions that add different features, but as you might expect, newer versions require newer operating systems. Windows XP will read up to version 2.01 out of the box, though some Blu-Ray drive manufacturers have released drivers for newer versions.

I formatted my most recently-purchased USB stick on Fedora. First off, I blew away the partition table and all traces of the FAT32 filesystem it came with:

# dd if=/dev/zero of=/dev/sdb bs=1M count=1
# wipefs -a /dev/sdb

Fedora uses the mkudffs command for creating UDF filesystems, which is part of the udftools package:

# yum install udftools
# mkudffs --revision=0x0201 --media-type=hd /dev/sdb

That’s it! Now the disk seems to be usable on Fedora, OS X, and Windows, which covers just about all of my computers. I will test OpenBSD one of these days.

There are undoubtedly ways to do this on other operating systems. Feel free to comment with instructions for your favorite operating system if you know them.