Use this information to upgrade from Search Services 1.x to Search Services 2.0.
Note: A reindex is required when you upgrade from Search Services 1.x to
Search Services 2.0. solr.content.dir is no longer used from Search
Services 2.0 and above. Solr itself provides that storage facility which means it
can be safely removed, which we recommend, for more see Search Services externalized configuration. If it is necessary for you to have a backup of the
old index and content store then it must be copied elsewhere before you
reindex.