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Chapter 1. GFS Overview
1.3.1. Cluster Volume Management
Cluster volume management provides simplified management of volumes and the ability to dynam-
ically extend file system capacity without interrupting file-system access. With cluster volume man-
agement, you can aggregate multiple physical volumes into a single, logical device across all nodes in
a cluster.
Cluster volume management provides a logical view of the storage to GFS, which provides flexibility
for the administrator in how the physical storage is managed. Also, cluster volume management pro-
vides increased availability because it allows increasing the storage capacity without shutting down
the cluster. Refer to Chapter 5 Using the Pool Volume Manager for more information about cluster
volume management.
1.3.2. Lock Management
A lock management mechanism is a key component of any cluster file system. The GFS OmniLock
architecture provides the following lock managers:
Single Lock Manager (SLM) — A simple centralized lock manager that can be configured to run
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either on a file system node or on a separate dedicated lock manager node.
Redundant Lock Manager (RLM) — A high-availability lock manager. It allows the configuration
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of a master and multiple hot-standby failover lock manager nodes. The failover nodes provide
failover in case the master lock manager node fails.
The lock managers also provide cluster management functions that control node recovery. Refer to
Chapter 8 Using Clustering and Locking Systems for a description of the GFS lock protocols.
1.3.3. Cluster Management, Fencing, and Recovery
Cluster management functions in GFS monitor node status through heartbeat signals to determine
cluster membership. Also, cluster management keeps track of which nodes are using each GFS file
system, and initiates and coordinates the recovery process when nodes fail. This process involves
recovery coordination from the fencing system, the lock manager, and the file system. The cluster
management functions are embedded in each of the lock management modules described earlier in
Lock Management. Refer to Chapter 8 Using Clustering and Locking Systems for more information
on cluster management.
Fencing is the ability to isolate or "fence off" a cluster node when that node loses its heartbeat no-
tification with the rest of the cluster nodes. Fencing ensures that data integrity is maintained during
the recovery of a failed cluster node. GFS supports a variety of automated fencing methods and one
manual method. In addition, GFS provides the ability to configure each cluster node for cascaded
fencing with the automated fencing methods. Refer to Chapter 10 Using the Fencing System for more
information about the GFS fencing capability.
Recovery is the process of controlling reentry of a node into a cluster after the node has been fenced.
Recovery ensures that storage data integrity is maintained in the cluster while the previously fenced
node is reentering the cluster. As stated earlier, recovery involves coordination from fencing, lock
management, and the file system.
1.3.4. Cluster Configuration Management
Cluster configuration management provides a centralized mechanism for the configuration and
maintenance of configuration files throughout the cluster. It provides high-availability access to
configuration-state information for all nodes in the cluster.
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