This guide gives you some handy hints to upgrade from an archiva 1.0.x instance to a version 1.1.x.
It describes where settings in archiva 1.0.x are stored in archiva 1.1.x, which ones have to be kept, updated or removed...

Repositories

Keep your repositories content and delete the .index directories of your respective managed repositories, and execute the repository and database scanners after starting Archiva.

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