Atomic Recovery Units: Failure Atomicity for Logical Disks

Atomic recovery units (ARUs) are a mechanism that allows several logical disk operations to be executed as a single atomic unit with respect to failures. For example, ARUs can be used during file creation to update several pieces of file meta-data atomically. ARUs simplify file systems, as they isolate issues of atomicity within the logical disk system. ARUs are designed as part of the Logical Disk (LD), which provides an interface to disk storage that separates file and disk management by using logical block numbers and block lists. This paper discusses the semantics of concurrent ARUs, as well as the concurrency control they require. A prototype implementation in a log-structured logical disk system is presented and evaluated. The performance evaluation shows that the run-time overhead to support concurrent ARUs is negligible for Read and Write operations, and small but pronounced for file creation (4.0%–7.2%) and deletion (17.9%–20.5%), which mainly manipulate meta-data. The low overhead (when averaged over file creation, writing, reading, and deletion) for concurrent ARUs shows that issues of atomicity can be successfully isolated within the disk