Originally posted by chithanh
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Summary:
- Until 2013, UDF on Linux would incorrectly claim the filesystem was full for storage media >64GB
- POSIX permissions is a mute point for UDF in regards to portable storage as both users need mounting of it configured appropriately, the default automount support tends to ignore it otherwise.
- Block size logic for UDF has varied with previous kernels, but now expects logical sector size, typically this will be 512 blocks, for modern Windows and Linux(not sure about macOS), you should be able to use 4k blocks if the device is 4kn(which is only certain HDDs afaik, SSDs still offer 512e?). Therefore max capacity for UDF in a portable cross-OS storage media, is 2TiB(or 16TiB on 4kn), exFAT can achieve up to 128PiB by comparison.
- Only 127 unicode or 254 ASCII characters for max file name length, FAT32/exFAT/NTFS can all handle 255 unicode.
- Apple apparently made changes in 2018 and the UDF support got worse with High Sierra or just doesn't exist anymore? A user was able to do it via a third-party UDF driver from Sony.
From others in the discussion:
- > Which is not UDFs fault, but how it's implemented. It's not supposed to be partitioned at all and Linux can handle that fine. I think Windows just can't handle HDDs without a partition table though… maybe because of how it assigns drive letters or something. - Source
- > All platforms' UDF implementations are lacking in one way or another. None of them has a complete, proper implementation. Linux has no way to repair a broken UDF disk for example, but Windows also expects a specific setup and their repair tool sometimes even makes it worse. - Source(Same as prior)
- > The best option should be a single UDF 1.50 partition spanning the whole removable flash drive and including an MBR record in the first - Source
- > The broader problem with UDF on non-optical media is expectations about partitioning. One of Windows and macOS wants UDF inside a partition; the other wants it on the raw device itself. Linux doesn't care either way - Source
The useful format-udf tool points out further differences to keep in mind when choosing UDF as a cross-platform FS for portable storage. Worth noting:
- Windows expects a partition table for HDDs(unclear about SSDs), but Flash Drives do not.
- macOS expects a full disk to be UDF, not just a partition.
Not that exFAT is perfect, but far less hassle as you don't need to be aware of all those gotchas with UDF. Have had exFAT corrupt itself though, so it's only really useful for temporary cross-platform portable data, not reliable external storage. Useful for portable storage as it likely sees better performance when it comes to transferring data to/from the device vs UDF, due to better block size support.
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