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I see that mkudffs has options for four different identifiers: the logical volume (--lvid), the volume (--vid), the volume set (--vsid), and the file set identifier (--fsid). It, however, gives no guidance to what those mean.

So, I went to the UDF specs. Starting with ISO/IEC 13346 aka ECMA-167, I find that:

10.1.4 Volume Identifier (BP 24)

This field shall specify an identification of the volume.

14.1.10 Logical Volume Identifier (BP 112)

This field shall specify an identification of the logical volume on which the file set is recorded.

14.1.12 File Set Identifier (BP 304)

This field shall specify an identification of the file set described by this File Set Descriptor.

Well, that was useful.

So, I tried the OSTA UDF Spec 1.02, as that is the UDF version I'm trying to generate. It didn't help much (though did caution me against "fixed or trivial values").

I tried the UDF 1.50 specification which further tells me me—in §4.1—that before displaying those values, that an OS-specific transform using algorithms described in §4.1.2.1 must be applied. Of course, the next section after §4.1 is §4.2, so good luck on that. Also, the LogicalVolumeIdentifier is "extremely important in logical volume identification when multiple media are present within a jukebox. The name is typically what is displayed to the user."

So, I try the UDF 2.01 specification, and now I know that By now at least they've realized it's 4.2.2.1, which does exist, but doesn't help (it deals with stuff like character sets).

So, so far as I can tell:

  • The Logical Volume Identifier is what is displayed to the user (possibly only be jukeboxes). So it should be set to something meaningful, e.g., the disc title. I assume this is the disc title that Windows, Mac OS, or Nautilus would display.
  • The others exist only to waste space on the disc, having no actual description of what they're for. Despite that, I should set them to values which are neither fixed nor trivial. Possibly, I should just set them to random (i.e., not fixed) lines from Shakespeare (i.e., not trivial).

Or, better yet: what are the other fields for?

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Use UUIDs, not Shakespeare lines. –  Daniel Beck Dec 11 '11 at 10:13
    
@DanielBeck: Well, there is a note about the VolumeSetIdentifier field, which says the first 16 should be unique, the first 8 of those being a timestamp... So I guess for that one, UUID isn't allowed, but then again neither is Shakespeare. I do worry, though, that UUIDs may be considered "trivial". :-P On a serious note, I suspect the volume set stuff is similar in purpose to the volume set stuff in ISO9660, IOW, something no one uses, but the committee added anyway. –  derobert Dec 11 '11 at 10:42

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