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1.5. Red Hat Global File System

This section provides an overview of Red Hat GFS (Global File System). Two GFS file systems are available with Red Hat Cluster Suite: GFS and GFS2. For specific details about each one, refer to Global File System: Configuration and Administration and Global File System 2: Configuration and Administration.
GFS/GFS2 is a native file system that interfaces directly with the Linux kernel file system interface (VFS layer). When implemented as a cluster file system, GFS/GFS2 employs distributed metadata and multiple journals. Red Hat supports the use of GFS/GFS2 file systems only as implemented in Red Hat Cluster Suite.


Although a GFS/GFS2 file system can be implemented in a standalone system or as part of a cluster configuration, for the RHEL 5.5 release and later, Red Hat does not support the use of GFS/GFS2 as a single-node file system. Red Hat does support a number of high-performance single-node file systems that are optimized for single node, and thus have generally lower overhead than a cluster file system. Red Hat recommends using those file systems in preference to GFS/GFS2 in cases where only a single node needs to mount the file system.
Red Hat will continue to support single-node GFS/GFS2 file systems for existing customers.


The maximum number of nodes supported in a Red Hat Cluster deployment of GFS/GFS2 is 16.
GFS/GFS2 is based on a 64-bit architecture, which can theoretically accommodate an 8 EB file system. However, the maximum size of a GFS/GFS2 file system supported by Red Hat is 25 TB. If your system requires GFS/GFS2 file systems larger than 25 TB, contact your Red Hat service representative.
Red Hat GFS/GFS2 nodes can be configured and managed with Red Hat Cluster Suite configuration and management tools. Red Hat GFS/GFS2 then provides data sharing among GFS/GFS2 nodes in a Red Hat cluster, with a single, consistent view of the file system name space across the GFS/GFS2 nodes. This allows processes on multiple nodes to share GFS/GFS2 files the same way that processes on a single node can share files on a local file system, with no discernible difference.
A GFS/GFS2 file system must be created on an LVM logical volume that is a linear or mirrored volume. LVM logical volumes in a Red Hat Cluster are managed with CLVM (Cluster Logical Volume Manager). CLVM is a cluster-wide implementation of LVM, enabled by the CLVM daemon, clvmd, running in a Red Hat cluster. The daemon makes it possible to manage logical volumes via LVM2 across a cluster, allowing the cluster nodes to share the logical volumes. For information about the LVM volume manager, refer to Logical Volume Manager Administration.


When you configure a GFS/GFS2 file system as a cluster file system, you must ensure that all nodes in the cluster have access to the shared file system. Asymmetric cluster configurations in which some nodes have access to the file system and others do not are not supported.This does not require that all nodes actually mount the GFS/GFS2 file system itself.