Plugins for Orthanc. Those are heavily tailored to my needs. So don't come at me if they don't work for you (which they probably won't). Feel free to steal them, though..
Uses OrthancPluginRegisterStorageArea to "replace the built-in way Orthanc stores its files on the filesystem".
It stores files just like Orthanc in "StorageDirectory" and creates hardlinks to those files populating a directory given by "ShadowPath" with a structure of the form: [PatientName]/[StudyDate][StudyTime]/S[SequenceNumber]_[SequenceDescription]/[InstanceUID]`.
If "StorageDirectory" and "ShadowPath" are not on the same device, no shadow will be created.
The created links are removed, if the original file is removed via Orthanc. Empty directories are removed too.