2.4. Before Setting Up GFS

Before you install and set up GFS, note the following key characteristics of your GFS file systems:
GFS nodes
Determine which nodes in the Red Hat Cluster Suite will mount the GFS file systems.
Number of file systems
Determine how many GFS file systems to create initially. (More file systems can be added later.)
File system name
Determine a unique name for each file system. Each file system name is required in the form of a parameter variable. For example, this book uses file system names mydata1 and mydata2 in some example procedures.
File system size
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 for 64-bit hardware is 100 TB. The current supported maximum size of a GFS file system for 32-bit hardware is 16 TB. If your system requires larger GFS file systems, 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 requires, see Section 4.14, “Repairing a File System”.
Determine the number of journals for your GFS file systems. One journal is required for each node that mounts a GFS file system. Make sure to account for additional journals needed for future expansion, as you cannot add journals dynamically to a GFS file system.
GNBD server nodes
If you are using GNBD, determine how many GNBD server nodes are needed. Note the hostname and IP address of each GNBD server node for setting up GNBD clients later. For information on using GNBD with GFS, see the Using GNBD with Global File System document.
Storage devices and partitions
Determine the storage devices and partitions to be used for creating logical volumes (via CLVM) in the file systems.


You may see performance problems with GFS when many create and delete operations are issued from more than one node in the same directory at the same time. If this causes performance problems in your system, you should localize file creation and deletions by a node to directories specific to that node as much as possible.