Here’s what we were able to solve with help from Discovery. We’re on Mac systems.
mkltfs -d 0 -f -r size=10k/name=metadata.xml
mkdir /mnt/[LTO NAME]
ltfs /mnt/[LTO NAME]
This prepares the LTO to look for metadata.xml and put it in the index partition. You just copy the metadata.xml file along with all the other data and it will parse that one out. A good poor-man’s test to see if it’s in the index partition is to write it last. Then load the LTO and open the xml file. If it’s in the index, it will load right away. If it’s not, the tape will have to hunt for awhile to find it.