Windows – Convert NTFS to FAT32 without losing data

If you want to keep the data safe and do serious filesystem manipulation (which converting the FS certainly is), then first make a backup. Then test the backup.

Next you have three choices:

1. Boot windows (e.g. use someones computer) and use convert Driveletter: /fs:ntfs. (See http://support.microsoft.com/kb/307881 for more details).
2. Reformat the drive. You already have a known good backup and this is likely to be the fastest option. Then restore the data.
3. Find some utility which lets you convert under Linux. I never heard of one though and some quick googling did not find any.

You could probably do something like this:

Initial situation:
[-NTFS partition-----------------------------------------]

Shrink that partition to half the disk size
[-NTFS partition----------][ Unpartitioned---------------]

Now create a HFS partition in the unpartitioned space:
[-NTFS partition----------][ HFS+------------------------]

Copy over all data from the NTFS volume to the HFS volume.
Delete the NTFS volume, resulting in this:
[-unpartitioned-----------][ HFS+------------------------]

And finally grow the HFS volume

However I would never try this without having a backup.

And if you already have a backup then it is much faster to just delete the NTFS volume and create a HFS volume. Which means the best solution is to borrow some extra storage space.

Shrinking a NTFS volume can be done with windows (7 and upward) build in utilities or with external tools such as gparted, Ntfsresize, Symantec partition magic or many other tools.

Growing a HFS+ volume is possible with OS X,using the included Disk Utility app, located in /Applications/Utilities.

Copying over the data either requires an OS which has drivers for both NTFS and for HFS, or a third location with is understood by both. (e.g. a pen drive formatted to FAT32). Apple has a Bootcamp HFS driver which might be the easiest solution.