I get the impression that dbmarlin assumes that it is installed in /opt/dbmarlin (anyhow I got into trouble when I tried to use another directory). It would be nice if one could choose the location, or at least choose where postgres data resides. I can imagine that /opt is not dimensioned to hold an extra n00Gb of data for some installations. I had some space over in lvm so I added a new partition /opt/dbmarlin, but it may be a problem in certain setups.
It should be fairly easy to have a variable that points to /opt/dbmarlin and use that. It could then be easily overridden. I found 28 occurrences of /opt/dbmarlin:
find . -type f | xargs grep -I /opt/dbmarlin | wc -l
28