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(This is a follow-up to "What is the partition id / filesystem type for UDF?")

I know two ways to format a hard drive as UDF:

  • Windows Vista or later: "format x: /fs:UDF" (don't use /q ! )
  • Linux: "mkudffs --media-type=hd --blocksize=512 /dev/sdx"

The problem is that the 'other' OS does not recognize the disk as formatted at all: it simply refuses to mount it, no matter what commands I try.

How can I format a hard drive as UDF so that both Windows and Linux will be able to use it?

EDIT: updated the commands, now the result should work in either OS.

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The command you give works great on Linux. I formatted on Karmic, and can read and write under both Windows 7 and Karmic. –  Matt Joiner Dec 29 '09 at 13:44
Do not forget to zero the MBR first (dd if=/dev/zero of=/dev/sdx bs=512 count=1), to avoid confusion with any leftover partition table (since UDF does not use the first sector). –  CesarB Jan 2 '10 at 2:59
Related question: superuser.com/questions/39942/using-udf-on-a-usb-flash-drive –  CesarB Jan 2 '10 at 3:03
Thanks Skolima, this is great. Bye bye FAT32. I only need to be careful to stick to UDF version 2.01 and to 512 block size and I have the perfect hard disk partition shared across Linux and Windows. –  MarcH Dec 29 '11 at 23:46
for some strange reason you also need to create the partition from Windows. Not necessarily format it there but create it. –  MarcH Dec 30 '11 at 1:05

4 Answers 4

up vote 9 down vote accepted

It turns out that using the /q switch on Windows was the culprit: it enables 'quick format', i.e. the formatting process continues in background with every write made to the disk. Once it finishes, the drive is handled by Linux just fine.

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On the other hand, formatting with Linux' mkudffs seems to sucessfully complete in seconds. –  MarcH Dec 29 '11 at 23:41
I actually had to do a quick format in Win7 after creating the file system with mkudffs in Linux. Without that, Windows just kept wanting to format the drive. It ended up creating a 5MB empty space at the end of the drive, for whatever reason. But at least it works in both OS now. –  DanMan Nov 3 '12 at 23:41
In reply to myself: those 5MB might be the meta data block in recent UDF versions. –  DanMan Sep 8 '13 at 11:44

How did you reconcile your discovery in the previous question (that the UDF filesystem should be created on the whole disk, not a partition) with that Windows command ("format x: /fs:UDF")? In my attempts, Windows only gives drive letters to partitions.

As far as formatting for compatibility, I think the key is in the block size. Since most hard drives and USB flash sticks have a block size of 512 bytes, I've had the most compatibility when I create the FS that block size. I think format.com is using that block size, and mkudffs has a command switch for changing the block size. I could only get OS X and Windows to mount the filesystem when I used 512 byte blocks. Older versions of Linux assumed a block size of 2048, but you can always mount with "-o bs=512".

The whole disk vs partition issue still causes compatibility problems. Windows won't mount when I format the whole disk, and OS X doesn't look beyond the partition's type number when determining its filesystem, forcing me to mount it manually. Linux didn't care, as long as I gave it the appropriate device name (sda vs sda1).

In summary, the most compatible setup I've found is a singe partition of type 06(FAT16), formatted with UDF at block size 512. Works automatically on Windows, and a small bit of manual intervention on Linux and OS X.

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I've tried another experiment. This time I used a USB flash stick instead of a hard drive. Formatted with "mkudffs --media-type=hd --blocksize=512 /dev/sda", works without hassle on Linux, OS X, and Vista. Too bad Windows seems to allow partitionless formats on USB sticks but not hard drives. –  Simon Oct 9 '09 at 18:22
You definitely want to keep the same block size to avoid prematurely wearing the flash memory, see: lwn.net/Articles/428584 –  MarcH Dec 29 '11 at 1:22

Don't use UDF. I would have chosen either FAT32 or NTFS file system, which is visible from both linux and windows.

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How is UDF different in this regard? Is it not visible from Linux or Windows? –  Gerald Combs Aug 20 '09 at 22:29
FAT32 has a 4GB file size limit and does not store POSIX permissions. NTFS does not store POSIX permissions. I do need those features, and only UDF provides them. Besides, it is faster than NTFS. –  skolima Aug 24 '09 at 17:01
-1 because this is not an answer to the question. –  dolmen Jun 2 at 15:41
@skolima - What? That is like saying that you choose to raise Camels to generate milk without even considering Goats or Cows. There are way better file systems out there than UDF. –  djangofan Jun 2 at 15:54

UDF was designed for optical media, perhaps that's the problem?

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For initial revisions (before 1.5) this is true. However, later versions (those available in Linux and Windows Vista) are also meant to be used with random-rewrite media like hard drives. –  skolima Aug 17 '09 at 17:08
"UDF is a truly universal file system. It can be used on all kinds of optical media, including read only [...], write once [...], rewritable [...], and of course block device (hard drives)." From "Wenguang's Introduction to Universal Disk Format" –  fbmd Jan 20 at 9:30

protected by Mark Henderson Jul 12 '12 at 20:30

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