Described is a technology by which an owner node in a server cluster maintains ownership of a storage mechanism through a persistent reservation mechanism, while allowing non-owning nodes read and write access to the storage mechanism. An owner node writes a reservation key to a registration table associated with the storage mechanism. Non-owning nodes write a shared key that gives them read and write access. The owner node validates the shared keys against cluster membership data, and preempts (e.g., removes) any key deemed not valid. The owner node also defends ownership against challenges to ownership made by other nodes, so that another node can take over ownership if a (formerly) owning node is unable to defend, e.g., because of a failure.