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The Resilient Storage Add-On provides numerous file system capabilities for improving resiliency to system failure. GFS2 is a shared storage file system - often referred to as a cluster file system - that gives each server in a cluster direct access to a shared block device over a local storage area network (SAN) of up to 100 terabytes. Each member of the cluster has direct access to the same storage device, and all cluster nodes access the same set of files.
Because a clustered file system like GFS2 requires cache consistency to insure data consistency and integrity, there must be a single version of all files in a cluster visible to all nodes within that cluster. To prevent members of the cluster from updating the same storage block at the same time in a way that corrupts data, GFS2 uses a cluster-wide locking mechanism called Distributed Lock Manager (DLM) to arbitrate access to the storage as a concurrency control mechanism.