Cloud computing poses new challenges to data storage. While cloud providers use shared distributed hardware, which is inherently unreliable and insecure, cloud users expect their data to be safely and securely stored, available at any time, and accessible in the same way as their locally stored data. In this chapter, the authors present XtreemFS, a file system for the cloud. XtreemFS reconciles the need of cloud providers for cheap scale-out storage solutions with that of cloud users for a reliable, secure, and easy data access. The main contributions of the chapter are: a description of the internal architecture of XtreemFS, which presents an approach to build large-scale distributed POSIX-compliant file systems on top of cheap, off-the-shelf hardware; a description of the XtreemFS security infrastructure, which guarantees an isolation of individual users despite shared and insecure storage and network resources; a comprehensive overview of replication mechanisms in XtreemFS, which guarantee consistency, availability, and durability of data in the face of component failures; an overview of the snapshot infrastructure of XtreemFS, which allows to capture and freeze momentary states of the file system in a scalable and fault-tolerant fashion. The authors also compare XtreemFS with existing solutions and argue for its practicability and potential in the cloud storage market.
Introduction to Bigdata and Relation with IoT
