What options are there for migrating data from Subversion to IBM Rational ClearCase?
ClearCase does not provide a tool to import from Subversion to maintain version history.
If you are not interested in maintaining version history and merely wish to start from the latest version or a preselected configuration, you can use the clearfsimport command. Review the ClearCase Command Reference Guide on the topic of clearfsimport (cleartool man clearfsimport) for more information.
If you require version history, you may want to evaluate the open source tool svn2cc.
It is possible to create views in Subversion representing certain milestones in your development stream. From there you can import the versions from each view sequentially using the aforementioned command clearfsimport. The clearfsimport command in this scenario will create a new version of the element each time it is run applying a label to the imported versions automatically.