Gracefully degradable versioned storage systems

Abstract

Multiple versions of data on different sets of machines allow a system to degrade gracefully even when experiencing excessive failures. When excessive failures cause the latest versions to be unavailable, the system becomes degraded, but still offers an old version if available. A most recent coherent set of the available older versions is found and provided. The degree of degradation increases gradually as the system experiences more and more failures. Graceful degradation is desirably complementary to fault tolerance.

Dependencies are inferred from the claim text.