Red Hat ENTERPRISE LINUX 5 - GLOBAL FILE SYSTEM 2 Manual page 14

Chapter 1. GFS2 Overview
Context-Dependent Path Names
GFS2 file systems do not provide support for context-dependent path names, which allow you to
create symbolic links that point to variable destination files or directories. For this functionality in
GFS2, you can use the bind option of the mount command. For information on managing pathnames
Section 3.12, "Bind Mounts and Context-Dependent Path Names".
in GFS2, see
gfs2.ko Module
The kernel module that implements the GFS file system is gfs.ko. The kernel module that
implements the GFS2 file system is gfs2.ko.
Enabling Quota Enforcement in GFS2
In GFS2 file systems, quota enforcement is disabled by default and must be explicitly enabled.
To enable and disable quotas for GFS2 file systems, you use the quota=on|off|account
option for the mount command. For information on enabling and disabling quota enforcement, see
Section 3.5.4, "Enabling/Disabling Quota Enforcement".
Data Journaling
GFS2 file systems support the use of the chattr command to set and clear the j flag on a file or
directory. Setting the +j flag on a file enables data journaling on that file. Setting the +j flag on a
directory means "inherit jdata", which indicates that all files and directories subsequently created in
that directory are journaled. Using the chattr command is the preferred way to enable and disable
data journaling on a file.
Adding Journals Dynamically
In GFS file systems, journals are embedded metadata that exists outside of the file system, making it
necessary to extend the size of the logical volume that contains the file system before adding journals.
In GFS2 file systems, journals are plain (though hidden) files. This means that for GFS2 file systems,
journals can be dynamically added as additional servers mount a filesystem, as long as space remains
on the file system for the additional journals. For information on adding journals to a GFS2 file system,
Section 3.7, "Adding Journals to a File System".
see
atime_quantum parameter removed
The GFS2 file system does not support the atime_quantum tunable parameter, which can be used
by the GFS file system to specify how often atime updates occur. In its place GFS2 supports the
relatime and noatime mount options. The relatime mount option is recommended to achieve
similar behavior to setting the atime_quantum parameter in GFS.
The data= option of the mount command
When mounting GFS2 file systems, you can specify the data=ordered or data=writeback option
of the mount. When data=ordered is set, the user data modified by a transaction is flushed to the
disk before the transaction is committed to disk. This should prevent the user from seeing uninitialized
blocks in a file after a crash. When data=writeback is set, the user data is written to the disk at any
time after it is dirtied. This does not provide the same consistency guarantee as ordered mode, but it
should be slightly faster for some workloads. The default is ordered mode.
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