Gfs Overview - Red Hat ENTERPRISE LINUX 5 - GLOBAL FILE SYSTEM Manual

Chapter 1.

GFS Overview

The Red Hat GFS file system 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 employs distributed
metadata and multiple journals. Red Hat supports the use of GFS file systems only as implemented in
Red Hat Cluster Suite.
Note
Although a GFS 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 as a single-node file system. Red Hat does support a number of high-performance
single node file systems which are optimized for single node and thus have generally
lower overhead than a cluster filesystem. Red Hat recommends using these file systems
in preference to GFS in cases where only a single node needs to mount the file system.
Red Hat will continue to support single-node GFS file systems for existing customers.
Note
Red Hat does not support using GFS for cluster file system deployments greater than 16
nodes.
GFS is based on a 64-bit architecture, which can theoretically accommodate an 8 EB file system.
However, the current supported maximum size of a GFS file system is 25 TB. If your system requires
GFS file systems larger than 25 TB, contact your Red Hat service representative.
When determining the size of your file system, you should consider your recovery needs. Running the
gfs_fsck command on a very large file system can take a long time and consume a large amount
of memory. Additionally, in the event of a disk or disk-subsytem failure, recovery time is limited by
the speed of your backup media. For information on the amount of memory the gfs_fsck command
Section 3.14, "Repairing a File
requires, see
When configured in a Red Hat Cluster Suite, Red Hat GFS nodes can be configured and managed
with Red Hat Cluster Suite configuration and management tools. Red Hat GFS then provides data
sharing among GFS nodes in a Red Hat cluster, with a single, consistent view of the file system name
space across the GFS nodes. This allows processes on different nodes to share GFS files in the
same way that processes on the same node can share files on a local file system, with no discernible
difference. For information about Red Hat Cluster Suite refer to Configuring and Managing a Red Hat
Cluster.
While a GFS file system may be used outside of LVM, Red Hat supports only GFS file systems that
are created on a CLVM logical volume. CLVM is a cluster-wide implementation of LVM, enabled by the
CLVM daemon clvmd, which manages LVM logical volumes in a Red Hat Cluster Suite cluster. The
daemon makes it possible to use LVM2 to manage logical volumes across a cluster, allowing all nodes
in the cluster to share the logical volumes. For information on the LVM volume manager, see Logical
Volume Manager Administration
System".
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