The Red Hat GFS file system is a native file system that interfaces directly with the Linux kernel file system interface (VFS layer). A GFS file system can be implemented in a standalone system or as part of a cluster configuration. When implemented as a cluster file system, GFS employs distributed metadata and multiple journals.
A GFS file system can be created on an LVM logical volume. A logical volume is an aggregation of underlying block devices that appears as a single logical device. For information on the LVM volume manager, see the LVM Administrator's Guide.
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 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.
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.
LVM logical volumes in a Red Hat Cluster suite are managed with CLVM, which is a cluster-wide implementation of LVM, enabled by the CLVM daemon, clvmd running in a Red Hat Cluster Suite cluster. The daemon makes it possible to use LVM to manage logical volumes across a cluster, allowing all nodes in the cluster to share the logical volumes. to any directory on your system. For information on the LVM volume manager, see the LVM Administrator's Guide.
This chapter provides some basic, abbreviated information as background to help you understand GFS. It contains the following sections:
1.1. New and Changed Features
This section lists new and changed features included with the initial release of Red Hat Enterprise Linux 5.
GULM (Grand Unified Lock Manager) is not supported in Red Hat Enterprise Linux 5. If your GFS file systems use the GULM lock manager, you must convert the file systems to use the DLM lock manager. This is a two-part process.
While running Red Hat Enterprise Linux 4, convert your GFS file systems to use the DLM lock manager.
Upgrade your operating system to Red Hat Enterprise Linux 5, converting the lock manager to DLM when you do.
For information on upgrading to Red Hat Enterprise Linux 5 and converting GFS file systems to use the DLM lock manager, see Configuring and Managing a Red Hat Cluster.
Documentation for Red Hat Cluster Suite for Red Hat Enterprise Linux 5 has been expanded and reorganized. For information on the available documents, see
Section 2, “Related Documentation”.
