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Universal Disk Format (wikipedia.org)
10 points by doublextremevil on Jan 20, 2013 | hide | past | favorite | 10 comments

I'd be interested in hearing how successful a UDF-formatted USB stick would be in the real world. I managed to find a discussion on superuser from 2009:


One fairly big problem you have here is that there are going to be zillions of consumer devices that expect memory cards and USB sticks to be FAT32 and nothing else.

That really is the big problem. FAT32 won by being there at the right time.

Well, i just formatted my 32GB flash drive UDF, and no hiccups on mac or linux. The WDTV Live seems not to support it. Havent tested on Windows yet

I think the issue is not your computer, it's your camera and other random electronic appliances that support flash storage....

They tend to be very conservative about what they support, and have hard or impossible to update software.

NTFS support is better now than it was then. I think (but welcome corrections) that Windows, Linux (kernel) and OS X can all read and write NTFS now. There are extra drivers for OS X. I'm not sure what they provide. There is a problem with the lack of a real chkdsk outside of Windows. Sometimes the only advice to fix a problem is to run chkdsk in windows twice, but usually the problems that can be fixed by that are caused by people doing silly things like unplugging a drive while writing to it.

UDF on Wikipedia is interesting:


(EDIT: Wow, I didn't realise how much of it there is, and how bad my copy and paste is.)

* Maximum filename length: 255 bytes

* Allowable characters in directory entries: Any Unicode except NUL

* Maximum pathname length: 1,023 bytes

* Maximum file size: 16 EB

* Maximum volume size: 2 TB (hard disc) 8 TB (optical disc)

* Stores file owner: Yes

* POSIX file permissions: Yes

* Creation timestamps: Yes

* Last access/ read timestamps: Yes

* Last content modification timestamps: Unknown

* Disk copy created: Unknown

* Last metadata change timestamps: Yes

* Last archive timestamps: Yes

* Access control lists: Yes

* Security/ MAC labels: No

* Extended attributes/ Alternate data streams/ forks: Yes

* Checksum/ ECC: No

* Max timestamp granularity: unknown

Seems like a strange choice to have a maximum file size several orders of magnitude larger than your maximum volume size.

It's just a side effect. The maximum volume size is defined by the size of the (in practice, always fixed-size) word used to store a block address.

But generally files are stored as a tree or some other recursive data structure. If these have a limit at all it's either deliberately imposed (e.g. the triple-indirect block in a v7 Unix inode) or arbitrary (maximum depth of a maximally unablanced btree that fills the volume).

Basically, you have to limit your device size if you want sane block ID semantics. Files can be infinite if you want.

We've already reached the maximum volume size. Next!

ExFAT solves most of the major FAT32 problems (volume/file size), but it's patent encumbered:


Works on recent versions of Windows and OS X.

You can't use partitions with UDF.

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