Rio: Storing Files Reliably in Memory

Abstract: Memory is currently a second-class citizen of the storage hierarchy because of its vulnerability to power failures and software crashes. Designers have traditionally sacrificed either reliability or performance when using memory as a cache for disks; our goal is to do away with this tradeoff by making memory as reliable as disks. The Rio (RAM I/O) project at Michigan is modifying the Digital Unix (formerly OSF/1) kernel to protect the file cache from operating system crashes. If successful, making memory as reliable as disks will 1) improve file cache performance to that of a pure write-back scheme by eliminating all reliability-caused writes to disk; 2) improve reliability to that of a write-through scheme by making memory a reliable place to store files long term; and 3) simplify applications such as file systems and databases by eliminating write-back daemons and complex commit and checkpointing protocols.