Data Structure Consistency Using Atomic Operations in Storage Devices

Managing concurrency is a fundamental requirement for any multi-threaded system, frequently implemented by serializing critical code regions or using object locks on shared resources. Storage systems are one case of this, where multiple clients may wish to access or modify on-disk objects concurrently yet safely. Data consistency may be provided by an inter-client protocol, or it can be implemented in the file system server or storage device. In this work we demonstrate ways of enabling atomic operations on object-based storage devices (OSDs), in particular, the compare-and-swap and fetch-and-add atomic primitives. With examples from basic disk resident data structures to higher level applications like file systems, we show how atomics-capable storage devices can be used to solve consistency requirements of distributed algorithms. Offloading consistency management to storage devices obviates the need for dedicated lock manager servers.