Lock management is a common cluster-infrastructure service that provides a mechanism for other cluster infrastructure components to synchronize their access to shared resources. In a Red Hat cluster, DLM (Distributed Lock Manager) is the lock manager. As implied in its name, DLM is a distributed lock manager and runs in each cluster node; lock management is distributed across all nodes in the cluster (refer to Figure 1.2, “CMAN/DLM Overview”). GFS and CLVM use locks from the lock manager. GFS uses locks from the lock manager to synchronize access to file system metadata (on shared storage). CLVM uses locks from the lock manager to synchronize updates to LVM volumes and volume groups (also on shared storage).