This article documents how to change where the indexes are stored.
Resolution
Please see the excerpt from the portal.properties file about the lucene.store.type property:
Designate whether Lucene stores indexes in a file system or in RAM.
#
lucene.store.type=file
#lucene.store.type=ram
If the portal property is set to ram, whenever the server is restarted, the index is lost because storing the data in RAM is only meant for very quick access and not meant to carry over at server restart. One symptom of having the indexes set to ram is that a reindex is necessary everytime the server is started in order to view the list of users and organizations.