here - OSTA - Optical Storage Technology Association

Descriptors should be used. For example a Logical Volume created for a
jukebox.
NOTE: There is a benefit of using Long Allocation Descriptors even on a single
volume, which is the support of tracking erased extents on rewritable media. See
section 2.3.10.1 for additional information.
For both Short and Long Allocation Descriptors, if the 30 least significant bits of
the ExtentLength field is 0, then the 2 most significant bits shall be 0.
NOTE: For volumes in which a Virtual Partition Map is recorded:
• Allocation Descriptors identifying virtual space shall have an extent length
of theone block size or less. Allocation descriptors identifying file data,
directories, or stream data shall identify physical space. ICBs recorded in
virtual space shall use long_ad allocation descriptors to identify physical
space. The use of short_ad allocation descriptors would identify file data
in virtual space if the ICB were in virtual space.
• Descriptors recorded in virtual space shall have the virtual logical block
number recorded in the Tag Location field.
NOTE: For volumes in which a Metadata Partition Map is recorded:
• Allocation descriptors identifying directory or stream directory data shall
identify metadata space.
• Allocation descriptors identifying file or stream data shall identify physical
space.
• Allocation descriptors recorded in metadata space shall use SHORT_ADs
when identifying extents also in metadata space.
• Allocation descriptors having an extent type of 3 (continuation) shall
identify an extent in the same partition in which the type 3 descriptor itself
is recorded.
• Descriptors recorded in metadata space shall have their metadata space
logical block number recorded in their descriptor tag TagLocation field, if
applicable.
UDF 2.01
61
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