Safe Caching in a Distributed File System for Network Attached Storage

In a distributed file system built on network attached storage, client computers access data directly from shared storage, rather than submitting I/O requests through a server. Without a server marshaling access to data, if a computer fails or becomes isolated in a network partition while holding locks on cached data objects, those objects become inaccessible to other computers until a locking au-thority can guarantee that the lock holder will not again directly access these data. We describe a server that acts as the locking authority and implements a lease-based proto-col for revoking access to data objects locked by an isolated or failed computer. When a lease expires, the server can be assured that the client no longer acts on locked data, and can safely redistribute locks to other clients. During nor-mal operation, this protocol invokes no message overhead, and uses no memory and performs no computation at the locking authority. 1