A New Metadata Update Method for Fast Recovery of SSD Cache

In order to maintain data in an SSD (solid-state disk) cache durable after a crash or reboot, metadata information needs to be stored persistently in SSD. There are two typical metadata methods, update-write-update and write-update. While write-update method has one less SSD write operation than update-write-update for each write I/O, it limits the amount of cached data that can be used after a system crash. We present a design and implementation of a novel metadata update method for SSD cache, referred to as Lazy-Update Following an Update-Write (LUFUW). Our new metadata update method allows maximal amount of data in SSD cache available upon restart after a power failure or system crash with minimal additional writes to SSD. This capability makes restart run twice as fast as existing SSD caches such as Flash cache [1] that can only use dirty data in the cache after crash recovery. We present our prototype implementation on Linux kernel and performance measurements as compared with existing SSD cache solutions.