Description of problem:
A blueprint exists [1] to add support to Cinder for having a single volume attached to multiple compute instances, in support of other changes to the upstream vCenter driver [2].
Discussions at the Havana design summit pointed to the bulk of the work however being in Nova. Currently a design for this, and the associated work, does not appear to be tracked explicitly - though at least some of it may implicitly fall under the vCenter changes.
This bug is to track the need to resource further investigation and potentially propose a design upstream to move this feature request forward.
Additional info:
[1] https://blueprints.launchpad.net/cinder/+spec/multi-attach-volume
[2] https://blueprints.launchpad.net/nova/+spec/fc-support-for-vcenter-driver