Some notes in http://dspace.org/technology/system-docs/storage.html about backing up and restoring your Postgres database and the bitstream store.
Use import/export tools
In DSpace 1.7.0 and above, there is now an AIP (Archival Information Package) Backup and Restore process available. For more information see: AIP Backup and Restore
Back up the data using the batch item exporter. In other words, you'd use the batch item exporter to export all of the contents of your DSpace to location X, and back X up.