Minuet: Rethinking Concurrency Control in Storage Area Networks.

Clustered applications in storage area networks (SANs), widely adopted in enterprise datacenters, have traditionally relied on distributed locking protocols to coordinate concurrent access to shared storage devices. We examine the semantics of traditional lock services for SAN environments and ask whether they are sufficient to guarantee data safety at the application level. We argue that a traditional lock service design that enforces strict mutual exclusion via a globally-consistent view of locking state is neither sufficient nor strictly necessary to ensure application-level correctness in the presence of asynchrony and failures. We also argue that in many cases, strongly-consistent locking imposes an additional and unnecessary constraint on application availability. Armed with these observations, we develop a set of novel concurrency control and recovery protocols for clustered SAN applications that achieve safety and liveness in the face of arbitrary asynchrony, crash failures, and network partitions. Finally, we present and evaluate Minuet- a new synchronization primitive based on these protocols that can serve as a foundational building block for safe and highly-available SAN applications.