After I started running Linux and then Mac OS X, in addition to Windows, I started on a quest to find the universal filesystem. I had multiboot systems and external drives where I wanted to to be able to read and write disks under multiple operating systems.

The obvious choice is FAT32, the ubiquitous, lowest-common de­nom­i­na­tor filesystem. FAT32 is supported out-of-the-box by all major operating systems, digital cameras, and PDAs, so that’s a huge advantage. FAT32 also has major short­com­ings:

• Maximum file size is 4GB. I have ISOs, MPEGs, and other large files exceeding this limit.
• Frag­men­ta­tion happens too easily.
• Timestamps: accurate only to 2-second resolution. No notion of timezones or UTC.
• Journaling: none. Preferred for robustness.
• ACLs or Per­mis­sions. Nothing beyond R/W.

I ex­per­i­ment­ed with ext3 (and its non-journaling sibling, ext2) on Windows and later on the Mac. On Windows, ext2fs works well and I used it happily for several months on a machine du­al­boot­ing XP and Ubuntu. It did not work well with Vista initially, though that seems to have been fixed since.

My ex­pe­ri­ences on the Mac were bad: ext2fsx caused some kernel panics, which was enough for me to abandon it.

There was no free solution for reading and writing Mac HFS+ disks under Linux and Windows the last time that I checked.

Both Linux and Macs natively support mounting NTFS disks read-only. The NTFS-3G project allows Linux to write to NTFS disks, and Mac NTFS-3G does likewise for Macs. I’ve never had a problem with NTFS-3G and it’s worked flawlessly under Linux and Mac for me.