Description of problem: We would like to see a template based partition deployment for the overcloud nodes. That is a template with information on disk layout for the overcloud nodes. currently the whole disk image makes it necessary for the undercloud to have enough free space for director to expand the image. This is an issue with underclouds that have limited space due to being vms themselfs. I believe that it would be more in line with the way director works if the template was passed to director and it took care of partitioning the drive before applying the standard image. Then it could update links to the partitions on the OS.
This has been a recurring topic, but it was determined to require massive changes to ironic. Some of these changes have been done, so we can try revisiting it for OSP 16. I don't envision any practical way to backport it to 13 though. An alternative is to use the ansible deploy, but it's a TechPreview still: http://tripleo.org/install/advanced_deployment/ansible_deploy_interface.html.
Implementation notes: The feature as it is requested here will probably be implemented via deploy steps. The bare deploy steps framework has landed in Stein (15), but more work is planned in Train (16) to make it usable for cases like this. An actual deploy step to do custom partitioning is planned for the future, but is not currently on the Train (16) roadmap upstream. TripleO integration needed for us to use it is unlikely to land until 17. Realistically, I'd plan this as a stretch goal for 16 with a very high probability of slipping into 17+
*** This bug has been marked as a duplicate of bug 1381111 ***