Can I drop and re-create the DefaultQuadStorage? Currently system metadata consist of three "levels": QuadMapFormats are used to describe transformations of individual SQL values (or types of SQL values), QuadMaps refers to QuadMapFormats (via QuadMapValues) and describe some "minimal" independent RDB2RDF transformations, QuadStorages organizes QuadMaps. QuadStorages contains only "symlinks" to maps, if you drop a storage you don't drop all mappings inside. If you drop the DefaultQuadStorage or some other built-in thing, it can be safely recovered by DB.DBA.RDF_AUDIT_METADATA, with first parameter set to 1. This will keep your own data intact. However we recommend to write a script that declares all your formats, Linked Data Views and storages, to be able to reproduce the configuration after any failures. Related Virtuoso Tips and Tricks Collection SPARQL