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I have an external USB hard drive that I'd like to format to UDF for cross-compatibility with Windows and Macs. I tried exFAT, but for whatever reason, because of the block size (56KB) of the format, it's eaten up a huge portion of the disk space (~400GB actual data, ~900GB used disk space).

Is there a utility on Mac OS X to format hard drives to UDF?

I can't find any built-in to my version (OS X 10.8.2), and mkudffs doesn't appear to be in my $PATH, so I'm not sure where to go from here.

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OS X is supposed to fully support NTFS since Snow Leopard (fully updated), and anything newer. If I were you, I would go with that, unless you use Macs with older OS versions. Sounds simpler. – Ariane Feb 21 '13 at 1:15
@Ariane It doesn't support writing to NTFS, only reading. – Tyilo Feb 24 '13 at 17:43
@Tyilo… Looks like you need a third-party thingie. – Ariane Feb 24 '13 at 21:58
@Ariane I'm aware of those products, however I wanted to point out that OS X doesn't support NTFS-writing out of the box. – Tyilo Feb 24 '13 at 22:04
@Tyilo Yeah, sorry. An article I'd read sort of implied that, but looks like I'd interpreted it wrong. – Ariane Feb 24 '13 at 22:07

Using the Terminal, you might be able to format a disk into UDF. I use the following command to format Blu-Ray-Disks:

newfs_udf -v "Untitled UDF" -r 2.60 /dev/diskX

You might want to first find out under what device name your actual disk is found.

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I put it on Github. – aross Nov 22 '13 at 14:36
Revision 2.60 of UDF wastes space with an additional partition for metadata. This feature is useful to increase performance for DVD/BD media, but it is useless on hard disk and flash as it will reduce write performance. I recommend to use instead revision 2.01. – dolmen Jun 2 '14 at 21:18
Not to mention that revisions > 2.01 supposedly cannot be mounted in read-write on Linux. – Tobia Oct 18 '14 at 20:27

Someone did some research into how to format a flash drive with udf so it can be used on as many operating systems as possible. His findings are at and there's a script to format the disk properly at

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is there an utility for windows to format a drive in udf like the perl script does? – Gianluca P. Mar 21 '14 at 21:14

I only know about ways to do it from Windows, but if you want to format from a Mac, I would avoid it. I would not format a drive into Universal Disk Format since it is mainly read only, and you can encounter some errors. I would suggest formatting it in NTFS seeing as Mac OS X is supposed to be able to see that format now.

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OS X normally mounts NTFS volumes readonly. You can replace the builtin NTFS driver with one that handles writing, but I don't know how solid that is... – Gordon Davisson Feb 21 '13 at 16:16
-1 because you're claiming it is mainly read only, and you can encounter some errors without backing your statement with references. – dolmen Jun 2 '14 at 21:20

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