1. A method, comprising: representing a plurality of storage devices as resources of a cluster, to a cluster resource manager executing within the cluster, that manages cluster resources on a plurality of cluster nodes, the cluster resource manager executing as a user-level application; receiving, at a kernel-level storage driver executing within the cluster, a request from a client outside the cluster for a failover operation with respect to one of the plurality of storage devices, the failover operation requested by the client in response to the client detecting that a failure relating to the plurality of storage devices has occurred; in response to the request, causing the cluster resource manager to initiate the failover operation; and providing, before the failover operation has been performed, a response to the client indicating that the request has been processed.