Event-notification-based inactive file search for large-scale file systems

Finding inactive files is a challenging task in large-scale file systems. In a hierarchical storage management system or a cloud storage gateway system, inactive files are migrated to lower tiers to reduce the storage cost. Inactive files can also be applied the data reduction techniques such as deduplication and compression. Existing metadata search methods, using either file system crawling or metadata indexing, degrade file access performance because they require a large number of disk I/Os. The two-phase refining (TPR) we propose here searches for inactive files effectively by using file system event notification and pseudo-LRU lists. TPR consists of two processes: a listing process that lists the files created each day, and a searching process that refines files from the oldest pseudo-LRU list in order to identify files that can be migrated or subjected to data reduction technologies. Experimental results show that our method is superior to existing methods in terms of search time, file access performance, and space overhead.