If a module cannot be found in the workspace, the subversion plugin currently deletes the whole workspace and then checks out each and every module again...
The old behaviour is espacially annoying when the subversion module you already checked out are 20GB (for example libs).
This is a patch which fixes the problem. With the patch, subversion plugin will first try to checkout the module instead of deleting the whole workspace. Use patch on subversion/src/main/java/hudson/scm/subversion/UpdateUpdater.java

Thank you!