XtreemFS is an object-based, distributed file system for wide area networks. XtreemFS' outstanding feature is full (all components) and real (all failure scenarios, including network partitions) fault tolerance, while maintaining POSIX file system semantics. Fault-tolerance is achieved by using Paxos-based lease negotiation algorithms and is used to replicate files and metadata. SSL and X.509 certificates support make XtreemFS usable over public networks.