The ClusterHQ guys behind the FlockerHQ found this out the hard way [0]. Initially Flocker was meant to provide a container data migration tool on top of ZFS, now it is a front-end to more established storage systems like Cinder,vSan,EBS,GPD and so on.

[0] https://docs.clusterhq.com/en/latest/faq/#what-happened-to-z...