Red Hat ENTERPRISE LINUX 5 - GLOBAL FILE SYSTEM 2, Global File System 2 User Manual

Red Hat Enterprise Linux 5

Global File System 2

Red Hat Global File System 2

Global File System 2

Red Hat Enterprise Linux 5 Global File System 2
Red Hat Global File System 2
Edition 7

Copyright © 2010 Red Hat Inc..

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This book provides information about configuring and maintaining Red Hat GFS2 (Red Hat Global File
System 2) for Red Hat Enterprise Linux 5.

iii

Introduction v

1. Audience ........................................................................................................................ v

2. Related Documentation ................................................................................................... v

3. Feedback ....................................................................................................................... vi

4. Document Conventions ................................................................................................... vi

4.1. Typographic Conventions ..................................................................................... vi

4.2. Pull-quote Conventions ....................................................................................... viii

4.3. Notes and Warnings ........................................................................................... viii

1. GFS2 Overview 1

1.1. Before Setting Up GFS2 ............................................................................................... 2

1.2. Differences between GFS and GFS2 ............................................................................ 3

1.2.1. GFS2 Command Names .................................................................................... 3

1.2.2. Additional Differences Between GFS and GFS2 .................................................. 3

1.2.3. GFS2 Performance Improvements ...................................................................... 5

2. Getting Started 7

2.1. Prerequisite Tasks ........................................................................................................ 7

2.2. Initial Setup Tasks ........................................................................................................ 7

3. Managing GFS2 9

3.1. Making a File System ................................................................................................... 9

3.2. Mounting a File System .............................................................................................. 12

3.3. Unmounting a File System .......................................................................................... 15

3.4. Special Considerations when Mounting GFS2 File Systems .......................................... 15

3.5. GFS2 Quota Management .......................................................................................... 15

3.5.1. Setting Quotas ................................................................................................ 16

3.5.2. Displaying Quota Limits and Usage .................................................................. 17

3.5.3. Synchronizing Quotas ...................................................................................... 18

3.5.4. Enabling/Disabling Quota Enforcement ............................................................. 19

3.5.5. Enabling Quota Accounting .............................................................................. 20

3.6. Growing a File System ............................................................................................... 21

3.7. Adding Journals to a File System ................................................................................ 22

3.8. Data Journaling .......................................................................................................... 24

3.9. Configuring atime Updates ........................................................................................ 25

3.9.1. Mount with relatime ..................................................................................... 25

3.9.2. Mount with noatime ....................................................................................... 26

3.10. Suspending Activity on a File System ........................................................................ 26

3.11. Repairing a File System ............................................................................................ 27

3.12. Bind Mounts and Context-Dependent Path Names ..................................................... 29

3.13. Bind Mounts and File System Mount Order ................................................................ 30

3.14. The GFS2 Withdraw Function ................................................................................... 32

A. Converting a File System from GFS to GFS2 35

B. Revision History 37

Index 39

iv

v

Introduction

This book provides information about configuring and maintaining Red Hat GFS2 (Red Hat Global File
System 2). Red Hat GFS2 can be run in RHEL 5.3 and later. For the RHEL 5.5 release and later, Red
Hat does not support the use of GFS2 as a single-node file system. For information about Red Hat
Cluster Suite see Red Hat Cluster Suite Overview and Configuring and Managing a Red Hat Cluster.

HTML and PDF versions of all the official Red Hat Enterprise Linux manuals and release notes are
available online at http://www.redhat.com/docs/.

1. Audience

This book is intended primarily for Linux system administrators who are familiar with the following
activities:

• Linux system administration procedures, including kernel configuration

• Installation and configuration of shared storage networks, such as Fibre Channel SANs

2. Related Documentation

For more information about using Red Hat Enterprise Linux, refer to the following resources:

• Red Hat Enterprise Linux Installation Guide — Provides information regarding installation of Red
Hat Enterprise Linux.

• Red Hat Enterprise Linux Deployment Guide — Provides information regarding the deployment,
configuration and administration of Red Hat Enterprise Linux 5.

For more information about Red Hat Cluster Suite, refer to the following resources:

• Red Hat Cluster Suite Overview — Provides a high level overview of the Red Hat Cluster Suite.

• Configuring and Managing a Red Hat Cluster — Provides information about installing, configuring
and managing Red Hat Cluster components.

• Logical Volume Manager Administration — Provides a description of the Logical Volume Manager
(LVM), including information on running LVM in a clustered environment.

• Global File System: Configuration and Administration — Provides information about installing,
configuring, and maintaining Red Hat GFS (Red Hat Global File System).

• Using Device-Mapper Multipath — Provides information about using the Device-Mapper Multipath
feature of Red Hat Enterprise Linux.

• Using GNBD with Global File System — Provides an overview on using Global Network Block
Device (GNBD) with Red Hat GFS.

• Linux Virtual Server Administration — Provides information on configuring high-performance
systems and services with the Linux Virtual Server (LVS).

• Red Hat Cluster Suite Release Notes — Provides information about the current release of Red Hat
Cluster Suite.

Introduction

vi

Red Hat Cluster Suite documentation and other Red Hat documents are available in HTML,
PDF, and RPM versions on the Red Hat Enterprise Linux Documentation CD and online at http://

www.redhat.com/docs/.

3. Feedback

If you spot a typo, or if you have thought of a way to make this manual better, we would love to
hear from you. Please submit a report in Bugzilla (http://bugzilla.redhat.com/bugzilla/) against the
component Documentation-cluster.

Be sure to mention the manual's identifier:

rh-gfs2(EN)-5 (2010-03-12T15:15)

By mentioning this manual's identifier, we know exactly which version of the guide you have.

If you have a suggestion for improving the documentation, try to be as specific as possible. If you have
found an error, please include the section number and some of the surrounding text so we can find it
easily.

4. Document Conventions

This manual uses several conventions to highlight certain words and phrases and draw attention to
specific pieces of information.

In PDF and paper editions, this manual uses typefaces drawn from the Liberation Fonts1 set. The
Liberation Fonts set is also used in HTML editions if the set is installed on your system. If not,
alternative but equivalent typefaces are displayed. Note: Red Hat Enterprise Linux 5 and later includes
the Liberation Fonts set by default.

4.1. Typographic Conventions

Four typographic conventions are used to call attention to specific words and phrases. These
conventions, and the circumstances they apply to, are as follows.

Mono-spaced Bold

Used to highlight system input, including shell commands, file names and paths. Also used to highlight
keycaps and key combinations. For example:

To see the contents of the file my_next_bestselling_novel in your current
working directory, enter the cat my_next_bestselling_novel command at the
shell prompt and press Enter to execute the command.

The above includes a file name, a shell command and a keycap, all presented in mono-spaced bold
and all distinguishable thanks to context.

Key combinations can be distinguished from keycaps by the hyphen connecting each part of a key
combination. For example:

1

https://fedorahosted.org/liberation-fonts/

Typographic Conventions

vii

Press Enter to execute the command.

Press Ctrl+Alt+F1 to switch to the first virtual terminal. Press Ctrl+Alt+F7 to
return to your X-Windows session.

The first paragraph highlights the particular keycap to press. The second highlights two key
combinations (each a set of three keycaps with each set pressed simultaneously).

If source code is discussed, class names, methods, functions, variable names and returned values
mentioned within a paragraph will be presented as above, in mono-spaced bold. For example:

File-related classes include filesystem for file systems, file for files, and dir for
directories. Each class has its own associated set of permissions.

Proportional Bold

This denotes words or phrases encountered on a system, including application names; dialog box text;
labeled buttons; check-box and radio button labels; menu titles and sub-menu titles. For example:

Choose System → Preferences → Mouse from the main menu bar to launch Mouse

Preferences. In the Buttons tab, click the Left-handed mouse check box and click
Close to switch the primary mouse button from the left to the right (making the mouse

suitable for use in the left hand).

To insert a special character into a gedit file, choose Applications → Accessories
→ Character Map from the main menu bar. Next, choose Search → Find… from

the Character Map menu bar, type the name of the character in the Search field
and click Next. The character you sought will be highlighted in the Character Table.
Double-click this highlighted character to place it in the Text to copy field and then

click the Copy button. Now switch back to your document and choose Edit → Paste

from the gedit menu bar.

The above text includes application names; system-wide menu names and items; application-specific
menu names; and buttons and text found within a GUI interface, all presented in proportional bold and
all distinguishable by context.

Mono-spaced Bold Italic or Proportional Bold Italic

Whether mono-spaced bold or proportional bold, the addition of italics indicates replaceable or
variable text. Italics denotes text you do not input literally or displayed text that changes depending on
circumstance. For example:

To connect to a remote machine using ssh, type ssh [e-mail] at
a shell prompt. If the remote machine is example.com and your username on that
machine is john, type ssh [e-mail].

The mount -o remount file-system command remounts the named file
system. For example, to remount the /home file system, the command is mount -o
remount /home.

To see the version of a currently installed package, use the rpm -q package
command. It will return a result as follows: package-version-release.

Introduction

viii

Note the words in bold italics above — username, domain.name, file-system, package, version and
release. Each word is a placeholder, either for text you enter when issuing a command or for text
displayed by the system.

Aside from standard usage for presenting the title of a work, italics denotes the first use of a new and
important term. For example:

Publican is a DocBook publishing system.

4.2. Pull-quote Conventions

Terminal output and source code listings are set off visually from the surrounding text.

Output sent to a terminal is set in mono-spaced roman and presented thus:

books Desktop documentation drafts mss photos stuff svn
books_tests Desktop1 downloads images notes scripts svgs

Source-code listings are also set in mono-spaced roman but add syntax highlighting as follows:

package org.jboss.book.jca.ex1;

import javax.naming.InitialContext;

public class ExClient

{
public static void main(String args[])
throws Exception
{
InitialContext iniCtx = new InitialContext();
Object ref = iniCtx.lookup("EchoBean");
EchoHome home = (EchoHome) ref;
Echo echo = home.create();

System.out.println("Created Echo");

System.out.println("Echo.echo('Hello') = " + echo.echo("Hello"));
}
}

4.3. Notes and Warnings

Finally, we use three visual styles to draw attention to information that might otherwise be overlooked.

Note

Notes are tips, shortcuts or alternative approaches to the task at hand. Ignoring a note
should have no negative consequences, but you might miss out on a trick that makes your
life easier.

Important

Important boxes detail things that are easily missed: configuration changes that only
apply to the current session, or services that need restarting before an update will apply.

Notes and Warnings

ix

Ignoring a box labeled 'Important' won't cause data loss but may cause irritation and
frustration.

Warning

Warnings should not be ignored. Ignoring warnings will most likely cause data loss.

x

Chapter 1.

1

GFS2 Overview

The Red Hat GFS2 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, GFS2 employs distributed
metadata and multiple journals. Red Hat supports the use of GFS2 file systems only as implemented
in Red Hat Cluster Suite.

Note

Although a 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 GFS2 as a single-node file system. Red Hat does support a number of high­performance 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 GFS2 in cases where only a single node needs to mount the file
system.

Red Hat will continue to support single-node GFS2 file systems for existing customers.

Note

Red Hat does not support using GFS2 for cluster file system deployments greater than 16
nodes.

GFS2 is based on a 64-bit architecture, which can theoretically accommodate an 8 EB file system.
However, the current supported maximum size of a GFS2 file system is 25 TB. If your system requires
GFS2 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.gfs2 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 fsck.gfs2 command
requires, see Section 3.11, “Repairing a File System”.

When configured in a Red Hat Cluster Suite, Red Hat GFS2 nodes can be configured and managed
with Red Hat Cluster Suite configuration and management tools. Red Hat GFS2 then provides data
sharing among GFS2 nodes in a Red Hat cluster, with a single, consistent view of the file system
name space across the GFS2 nodes. This allows processes on different nodes to share GFS2 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 GFS2 file system may be used outside of LVM, Red Hats supports only GFS2 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

The gfs2.ko kernel module implements the GFS2 file system and is loaded on GFS2 cluster nodes.

Chapter 1. GFS2 Overview

2

Note

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

This chapter provides some basic, abbreviated information as background to help you understand
GFS2. It contains the following sections:

• Section 1.1, “Before Setting Up GFS2”

• Section 1.2, “Differences between GFS and GFS2”

1.1. Before Setting Up GFS2

Before you install and set up GFS2, note the following key characteristics of your GFS2 file systems:

GFS2 nodes

Determine which nodes in the Red Hat Cluster Suite will mount the GFS2 file systems.

Number of file systems

Determine how many GFS2 file systems to create initially. (More file systems can be added later.)

File system name

Determine a unique name for each file system. The name must be unique for all lock_dlm
filesystems over the cluster, and for all filesystems (lock_dlm and lock_nolock) on each local
node. 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.

Journals

Determine the number of journals for your GFS2 file systems. One journal is required for each
node that mounts a GFS2 file system. GFS2 allows you to add journals dynamically at a later
point as additional servers mount a filesystem. For information on adding journals to a GFS2 file
system, see Section 3.7, “Adding Journals to a 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 GFS2, 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.

Note

You may see performance problems with GFS2 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.

Differences between GFS and GFS2

3

1.2. Differences between GFS and GFS2

This section lists the improvements and changes that GFS2 offers over GFS.

Migrating from GFS to GFS2 requires that you convert your GFS file systems to GFS2 with the
gfs2_convert utility. For information on the gfs2_convert utility, see Appendix A, Converting a

File System from GFS to GFS2.

1.2.1. GFS2 Command Names

In general, the functionality of GFS2 is identical to GFS. The names of the file system commands,
however, specify GFS2 instead of GFS. Table 1.1, “GFS and GFS2 Commands” shows the equivalent
GFS and GFS2 commands.

GFS Command GFS2 Command Description

mount mount Mount a file system. The system can determine whether

the file system is a GFS or GFS2 file system type.
For information on the GFS2 mount options see the
gfs2_mount(8) man page.

umount umount Unmount a file system.

fsck
gfs_fsck

fsck
fsck.gfs2

Check and repair an unmounted file system.

gfs_grow gfs2_grow Grow a mounted file system.

gfs_jadd gfs2_jadd Add a journal to a mounted file system

gfs_mkfs
mkfs -t gfs

mkfs.gfs2
mkfs -t gfs2

Create a file system on a storage device.

gfs_quota gfs2_quota Manage quotas on a mounted file system.

gfs_tool gfs2_tool Configure, tune, or gather information about a file system.

gfs_edit gfs2_edit Display, print, or edit file system internal structures. The

gfs2_edit command can be used for GFS file systems

as well as GFS2 file system.

gfs_tool
setflag
jdata/
inherit_jdata

chattr +j

(preferred)

Enable journaling on a file or directory.

setfacl/
getfacl

setfacl/
getfacl

Set or get file access control list for a file or directory.

setfattr/
getfattr

setfattr/
getfattr

set or get the extended attributes of a file.

Table 1.1. GFS and GFS2 Commands

For a full listing of the supported options for the GFS2 file system commands, see the man pages for
those commands.

1.2.2. Additional Differences Between GFS and GFS2

This section summarizes the additional differences in GFS and GFS2 administration that are not
described in Section 1.2.1, “GFS2 Command Names”.

Chapter 1. GFS2 Overview

4

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
in GFS2, see Section 3.12, “Bind Mounts and Context-Dependent Path Names”.

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,
see Section 3.7, “Adding Journals to a File System”.

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.

GFS2 Performance Improvements

5

The gfs2_tool command

The gfs2_tool command supports a different set of options for GFS2 than the gfs_tool command
supports for GFS:

• The gfs2_tool command supports a journals parameter that prints out information about the
currently configured journals, including how many journals the file system contains.

• The gfs2_tool command does not support the counters flag, which the gfs_tool command
uses to display GFS statistics.

• The gfs2_tool command does not support the inherit_jdata flag. To flag a directory as
"inherit jdata", you can set the jdata flag on the directory or you can use the chattr command
to set the +j flag on the directory. Using the chattr command is the preferred way to enable and
disable data journaling on a file.

The gfs2_edit command

The gfs2_edit command supports a different set of options for GFS2 than the gfs_edit command
supports for GFS. For information on the specific options each version of the command supports, see
the gfs2_edit and gfs_edit man pages.

1.2.3. GFS2 Performance Improvements

There are many features of GFS2 filesystems that do not result in a difference in the user interface
from GFS file systems but which improve file system performance.

A GFS2 filesystem provides improved file system performance in the following ways:

• Better performance for heavy usage in a single directory.

• Faster synchronous I/O operations

• Faster cached reads (no locking overhead)

• Faster direct I/O with preallocated files (provided I/O size is reasonably large, such as 4M blocks)

• Faster I/O operations in general

• Execution of the df command is much faster, because of faster statfs calls.

• The atime mode has been improved to reduce the number of write I/O operations generated by
atime when compared with GFS.

GFS2 file systems provide broader and more mainstream support in the following ways.

• GFS2 is part of the upstream kernel (integrated into 2.6.19).

• GFS2 supports the following features:

• SELinux extended attributes.

• the lsattr() and chattr() attribute settings via standard ioctl() calls.

• nanosecond timestamps

A GFS2 file system provides the following improvements to the internal efficiency of the file system.

Chapter 1. GFS2 Overview

6

• GFS2 uses less kernel memory

• GFS2 requires no metadata generation numbers.

Allocating GFS2 metadata does not require reads. Copies of metadata blocks in multiple journals
are managed by revoking blocks from the journal before lock release.

• GFS2 includes a much simpler log manager that knows nothing about unlinked inodes or quota
changes.

• The gfs2_grow and gfs2_jadd commands use locking to prevent multiple instances running at
the same time.

• The ACL code has been simplified for calls like creat() and mkdir().

• Unlinked inodes, quota changes, and statfs changes are recovered without remounting the
journal.

Chapter 2.

7

Getting Started

This chapter describes procedures for initial setup of GFS2 and contains the following sections:

• Section 2.1, “Prerequisite Tasks”

• Section 2.2, “Initial Setup Tasks”

2.1. Prerequisite Tasks

Before setting up Red Hat GFS2, make sure that you have noted the key characteristics of the GFS2
nodes (refer to Section 1.1, “Before Setting Up GFS2”). Also, make sure that the clocks on the GFS2
nodes are synchronized. It is recommended that you use the Network Time Protocol (NTP) software
provided with your Red Hat Enterprise Linux distribution.

Note

The system clocks in GFS2 nodes must be within a few minutes of each other to prevent
unnecessary inode time-stamp updating. Unnecessary inode time-stamp updating
severely impacts cluster performance.

2.2. Initial Setup Tasks

Initial GFS2 setup consists of the following tasks:

1. Setting up logical volumes.

2. Making a GFS2 files system.

3. Mounting file systems.

Follow these steps to set up GFS2 initially.

1. Using LVM, create a logical volume for each Red Hat GFS2 file system.

Note

You can use init.d scripts included with Red Hat Cluster Suite to automate
activating and deactivating logical volumes. For more information about init.d
scripts, refer to Configuring and Managing a Red Hat Cluster.

2. Create GFS2 file systems on logical volumes created in Step 1. Choose a unique name for each
file system. For more information about creating a GFS2 file system, refer to Section 3.1, “Making

a File System”.

You can use either of the following formats to create a clustered GFS2 file system:

mkfs.gfs2 -p lock_dlm -t ClusterName:FSName -j NumberJournals BlockDevice

Chapter 2. Getting Started

8

mkfs -t gfs2 -p lock_dlm -t LockTableName -j NumberJournals BlockDevice

You can use either of the following formats to create a local GFS2 file system:

mkfs.gfs2 -p lock_nolock -j NumberJournals BlockDevice

mkfs -t gfs2 -p lock_nolock -j NumberJournals BlockDevice

For more information on creating a GFS2 file system, see Section 3.1, “Making a File System”.

3. At each node, mount the GFS2 file systems. For more information about mounting a GFS2 file
system, see Section 3.2, “Mounting a File System”.

Command usage:

mount BlockDevice MountPoint

mount -o acl BlockDevice MountPoint

The -o acl mount option allows manipulating file ACLs. If a file system is mounted without the ­o acl mount option, users are allowed to view ACLs (with getfacl), but are not allowed to set
them (with setfacl).

Note

You can use init.d scripts included with Red Hat Cluster Suite to automate
mounting and unmounting GFS2 file systems. For more information about init.d
scripts, refer to Configuring and Managing a Red Hat Cluster.

Chapter 3.

9

Managing GFS2

This chapter describes the tasks and commands for managing GFS2 and consists of the following
sections:

• Section 3.1, “Making a File System”

• Section 3.2, “Mounting a File System”

• Section 3.3, “Unmounting a File System”

• Section 3.5, “GFS2 Quota Management”

• Section 3.6, “Growing a File System”

• Section 3.7, “Adding Journals to a File System”

• Section 3.8, “Data Journaling”

• Section 3.9, “Configuring atime Updates”

• Section 3.10, “Suspending Activity on a File System”

• Section 3.11, “Repairing a File System”

• Section 3.12, “Bind Mounts and Context-Dependent Path Names”

• Section 3.13, “Bind Mounts and File System Mount Order”

• Section 3.14, “The GFS2 Withdraw Function”

3.1. Making a File System

You create a GFS2 file system with the mkfs.gfs2 command. You can also use the mkfs command
with the -t gfs2 option specified. A file system is created on an activated LVM volume. The following
information is required to run the mkfs.gfs2 command:

• Lock protocol/module name (the lock protocol for a cluster is lock_dlm)

• Cluster name (when running as part of a cluster configuration)

• Number of journals (one journal required for each node that may be mounting the file system)

When creating a GFS2 file system, you can use the mkfs.gfs2 command directly, or you can use the
mkfs command with the -t parameter specifying a filesystem of type gfs2, followed by the gfs2 file
system options.

Note

Once you have created a GFS2 file system with the mkfs.gfs2 command, you cannot
decrease the size of the file system. You can, however, increase the size of an existing
file system with the gfs2_grow command, as described in Section 3.6, “Growing a File

System”.

Chapter 3. Managing GFS2

10

Usage

When creating a clustered GFS2 filesystem, you can use either of the following formats:

mkfs.gfs2 -p LockProtoName -t LockTableName -j NumberJournals BlockDevice

mkfs -t gfs2 -p LockProtoName -t LockTableName -j NumberJournals BlockDevice

When creating a local GFS2 filesystem, you can use either of the following formats:

Note

For the RHEL 5.5 release and later Red Hat does not support the use of GFS2 as a
single-node file system. Red Hat will continue to support single-node GFS2 file systems
for existing customers.

mkfs.gfs2 -p LockProtoName -j NumberJournals BlockDevice

mkfs -t gfs2 -p LockProtoName -j NumberJournals BlockDevice

Warning

Make sure that you are very familiar with using the LockProtoName and
LockTableName parameters. Improper use of the LockProtoName and
LockTableName parameters may cause file system or lock space corruption.

LockProtoName

Specifies the name of the locking protocol to use. The lock protocol for a cluster is lock_dlm.

LockTableName

This parameter is specified for GFS2 filesystem in a cluster configuration. It has two parts
separated by a colon (no spaces) as follows: ClusterName:FSName

• ClusterName, the name of the Red Hat cluster for which the GFS2 file system is being

created.

• FSName, the file system name, can be 1 to 16 characters long. The name must be unique for all

lock_dlm filesystems over the cluster, and for all filesystems (lock_dlm and lock_nolock)
on each local node.

Number

Specifies the number of journals to be created by the mkfs.gfs2 command. One journal is
required for each node that mounts the file system. For GFS2 file systems, more journals can be
added later without growing the filesystem, as described in Section 3.7, “Adding Journals to a File

System”.

Examples

11

BlockDevice

Specifies a logical or physical volume.

Examples

In these examples, lock_dlm is the locking protocol that the file system uses, since this is a clustered
file system. The cluster name is alpha, and the file system name is mydata1. The file system
contains eight journals and is created on /dev/vg01/lvol0.

mkfs.gfs2 -p lock_dlm -t alpha:mydata1 -j 8 /dev/vg01/lvol0

mkfs -t gfs2 -p lock_dlm -t alpha:mydata1 -j 8 /dev/vg01/lvol0

In these examples, a second lock_dlm file system is made, which can be used in cluster alpha. The
file system name is mydata2. The file system contains eight journals and is created on /dev/vg01/
lvol1.

mkfs.gfs2 -p lock_dlm -t alpha:mydata2 -j 8 /dev/vg01/lvol1

mkfs -t gfs2 -p lock_dlm -t alpha:mydata2 -j 8 /dev/vg01/lvol1

Complete Options

Table 3.1, “Command Options: mkfs.gfs2” describes the mkfs.gfs2 command options (flags and

parameters).

Flag Parameter Description

-c Megabytes Sets the initial size of each journal's quota change file

to Megabytes.

-D Enables debugging output.

-h Help. Displays available options.

-J MegaBytes Specifies the size of the journal in megabytes. Default

journal size is 128 megabytes. The minimum size is
8 megabytes. Larger journals improve performance,
although they use more memory than smaller journals.

-j Number Specifies the number of journals to be created by the
mkfs.gfs2 command. One journal is required for

each node that mounts the file system. If this option is
not specified, one journal will be created. For GFS2 file
systems, you can add additional journals at a later time
without growing the file system.

-O Prevents the mkfs.gfs2 command from asking for
confirmation before writing the file system.

Chapter 3. Managing GFS2

12

Flag Parameter Description

-p LockProtoName Specifies the name of the locking protocol to use.

Recognized locking protocols include:
lock_dlm — The standard locking module, required
for a clustered file system.
lock_nolock — Used when GFS2 is acting as a local
file system (one node only).

-q Quiet. Do not display anything.

-r MegaBytes Specifies the size of the resource groups in megabytes.

The minimum resource group size is 32 MB. The
maximum resource group size is 2048 MB. A large
resource group size may increase performance on very
large file systems. If this is not specified, mkfs.gfs2
chooses the resource group size based on the size of
the file system: average size file systems will have 256
MB resource groups, and bigger file systems will have
bigger RGs for better performance.

-t LockTableName A unique identifier that specifies the lock table
field when you use the lock_dlm protocol; the
lock_nolock protocol does not use this parameter.
This parameter has two parts separated by a colon (no
spaces) as follows: ClusterName:FSName.
ClusterName is the name of the Red Hat cluster
for which the GFS2 file system is being created;
only members of this cluster are permitted to use
this file system. The cluster name is set in the /

etc/cluster/cluster.conf file via the Cluster
Configuration Tool and displayed at the Cluster
Status Tool in the Red Hat Cluster Suite cluster

management GUI.
FSName, the file system name, can be 1 to 16
characters in length, and the name must be unique
among all file systems in the cluster.

-u MegaBytes Specifies the initial size of each journal's unlinked tag
file.

-V Displays command version information.

Table 3.1. Command Options: mkfs.gfs2

3.2. Mounting a File System

Before you can mount a GFS2 file system, the file system must exist (refer to Section 3.1, “Making a

File System”), the volume where the file system exists must be activated, and the supporting clustering

and locking systems must be started (refer to Configuring and Managing a Red Hat Cluster). After
those requirements have been met, you can mount the GFS2 file system as you would any Linux file
system.

To manipulate file ACLs, you must mount the file system with the -o acl mount option. If a file
system is mounted without the -o acl mount option, users are allowed to view ACLs (with getfacl),
but are not allowed to set them (with setfacl).

Usage

13

Usage

Mounting Without ACL Manipulation

mount BlockDevice MountPoint

Mounting With ACL Manipulation

mount -o acl BlockDevice MountPoint

-o acl

GFS2-specific option to allow manipulating file ACLs.

BlockDevice

Specifies the block device where the GFS2 file system resides.

MountPoint

Specifies the directory where the GFS2 file system should be mounted.

Example

In this example, the GFS2 file system on /dev/vg01/lvol0 is mounted on the /mygfs2 directory.

mount /dev/vg01/lvol0 /mygfs2

Complete Usage

mount BlockDevice MountPoint -o option

The -o option argument consists of GFS2-specific options (refer to Table 3.2, “GFS2-Specific

Mount Options”) or acceptable standard Linux mount -o options, or a combination of both. Multiple

option parameters are separated by a comma and no spaces.

Note

The mount command is a Linux system command. In addition to using GFS2-specific
options described in this section, you can use other, standard, mount command options
(for example, -r). For information about other Linux mount command options, see the
Linux mount man page.

Table 3.2, “GFS2-Specific Mount Options” describes the available GFS2-specific -o option values

that can be passed to GFS2 at mount time.

Note

This table includes descriptions of options that are used with local file systems only For
the RHEL 5.5 release and later Red Hat does not support the use of GFS2 as a single-

Chapter 3. Managing GFS2

14

node file system. Red Hat will continue to support single-node GFS2 file systems for
existing customers.

Option Description

acl Allows manipulating file ACLs. If a file system is

mounted without the acl mount option, users are
allowed to view ACLs (with getfacl), but are not
allowed to set them (with setfacl).

data=[ordered|writeback] When data=ordered is set, the user data modified

by a transaction is flushed to the disk before the
transaction is commited to disk. This should prevent
the user from seeing uninitialized blocks in a file after a
crash. When data=writeback mode 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 value is ordered mode.

ignore_local_fs

Caution: This option should not be used
when GFS2 file systems are shared.

Forces GFS2 to treat the file system as a multihost file
system. By default, using lock_nolock automatically
turns on the localflocks flags.

localflocks

Caution: This option should not be used
when GFS2 file systems are shared.

Tells GFS2 to let the VFS (virtual file system) layer
do all flock and fcntl. The localflocks flag is
automatically turned on by lock_nolock.

lockproto=LockModuleName Allows the user to specify which locking protocol to

use with the file system. If LockModuleName is not
specified, the locking protocol name is read from the
file system superblock.

locktable=LockTableName Allows the user to specify which locking table to use

with the file system.

quota=[off/account/on] Turns quotas on or off for a file system. Setting the

quotas to be in the account state causes the per UID/
GID usage statistics to be correctly maintained by the
file system; limit and warn values are ignored. The
default value is off.

errors=panic|withdraw When errors=panic is specified, file system errors

will cause a kernel panic. The default behavior, which
is the same as specifying errors=withdraw, is for
the system to withdraw from the file system and make
it inaccessible until the next reboot; in some cases the
system may remain running. For information on the
GFS2 withdraw function, see Section 3.14, “The GFS2

Withdraw Function”.

Table 3.2. GFS2-Specific Mount Options

Unmounting a File System

15

3.3. Unmounting a File System

The GFS2 file system can be unmounted the same way as any Linux file system — by using the
umount command.

Note

The umount command is a Linux system command. Information about this command can
be found in the Linux umount command man pages.

Usage

umount MountPoint

MountPoint

Specifies the directory where the GFS2 file system is currently mounted.

3.4. Special Considerations when Mounting GFS2 File
Systems

GFS2 file systems that have been mounted manually rather than automatically through an entry in
the fstab file will not be known to the system when file systems are unmounted at system shutdown.
As a result, the GFS2 script will not unmount the GFS2 file system. After the GFS2 shutdown
script is run, the standard shutdown process kills off all remaining user processes, including the
cluster infrastructure, and tries to unmount the filesystem. This unmount will fail without the cluster
infrastructure and the system will hang.

To prevent the system from hanging when the GFS2 file systems are unmounted, you should do one
of the following:

• Always use an entry in the fstab file to mount the GFS2 file system.

• If a GFS2 file system has been mounted manually with the mount command, be sure to unmount
the file system manually with the umount command before rebooting or shutting down the system.

If your file system hangs while it is being unmounted during system shutdown under these
circumstances, perform a hardware reboot. It is unlikely that any data will be lost since the file system
is synced earlier in the shutdown process.

3.5. GFS2 Quota Management

File-system quotas are used to limit the amount of file system space a user or group can use. A user
or group does not have a quota limit until one is set. GFS2 keeps track of the space used by each user
and group even when there are no limits in place. GFS2 updates quota information in a transactional
way so system crashes do not require quota usages to be reconstructed.

To prevent a performance slowdown, a GFS2 node synchronizes updates to the quota file only
periodically. The "fuzzy" quota accounting can allow users or groups to slightly exceed the set limit.
To minimize this, GFS2 dynamically reduces the synchronization period as a "hard" quota limit is
approached.

Chapter 3. Managing GFS2

16

GFS2 uses its gfs2_quota command to manage quotas. Other Linux quota facilities cannot be used
with GFS2.

3.5.1. Setting Quotas

Two quota settings are available for each user ID (UID) or group ID (GID): a hard limit and a warn
limit.

A hard limit is the amount of space that can be used. The file system will not let the user or group use
more than that amount of disk space. A hard limit value of zero means that no limit is enforced.

A warn limit is usually a value less than the hard limit. The file system will notify the user or group
when the warn limit is reached to warn them of the amount of space they are using. A warn limit value
of zero means that no limit is enforced.

Limits are set using the gfs2_quota command. The command only needs to be run on a single node
where GFS2 is mounted.

By default, quota enforcement is not set on GFS2 file systems. To enable quota accounting, use the
quota= of the mount command when mounting the GFS2 file system, as described in Section 3.5.4,

“Enabling/Disabling Quota Enforcement”.

Usage

Setting Quotas, Hard Limit

gfs2_quota limit -u User -l Size -f MountPoint

gfs2_quota limit -g Group -l Size -f MountPoint

Setting Quotas, Warn Limit

gfs2_quota warn -u User -l Size -f MountPoint

gfs2_quota warn -g Group -l Size -f MountPoint

User

A user ID to limit or warn. It can be either a user name from the password file or the UID number.

Group

A group ID to limit or warn. It can be either a group name from the group file or the GID number.

Size

Specifies the new value to limit or warn. By default, the value is in units of megabytes. The
additional -k, -s and -b flags change the units to kilobytes, sectors, and file system blocks,
respectively.

MountPoint

Specifies the GFS2 file system to which the actions apply.

Displaying Quota Limits and Usage

17

Examples

This example sets the hard limit for user Bert to 1024 megabytes (1 gigabyte) on file system /
mygfs2.

gfs2_quota limit -u Bert -l 1024 -f /mygfs2

This example sets the warn limit for group ID 21 to 50 kilobytes on file system /mygfs2.

gfs2_quota warn -g 21 -l 50 -k -f /mygfs2

3.5.2. Displaying Quota Limits and Usage

Quota limits and current usage can be displayed for a specific user or group using the gfs2_quota
get command. The entire contents of the quota file can also be displayed using the gfs2_quota
list command, in which case all IDs with a non-zero hard limit, warn limit, or value are listed.

Usage

Displaying Quota Limits for a User

gfs2_quota get -u User -f MountPoint

Displaying Quota Limits for a Group

gfs2_quota get -g Group -f MountPoint

Displaying Entire Quota File

gfs2_quota list -f MountPoint

User

A user ID to display information about a specific user. It can be either a user name from the
password file or the UID number.

Group

A group ID to display information about a specific group. It can be either a group name from the
group file or the GID number.

MountPoint

Specifies the GFS2 file system to which the actions apply.

Command Output

GFS2 quota information from the gfs2_quota command is displayed as follows:

Chapter 3. Managing GFS2

18

user User: limit:LimitSize warn:WarnSize value:Value

group Group: limit:LimitSize warn:WarnSize value:Value

The LimitSize, WarnSize, and Value numbers (values) are in units of megabytes by default.
Adding the -k, -s, or -b flags to the command line change the units to kilobytes, sectors, or file
system blocks, respectively.

User

A user name or ID to which the data is associated.

Group

A group name or ID to which the data is associated.

LimitSize

The hard limit set for the user or group. This value is zero if no limit has been set.

Value

The actual amount of disk space used by the user or group.

Comments

When displaying quota information, the gfs2_quota command does not resolve UIDs and GIDs into
names if the -n option is added to the command line.

Space allocated to GFS2's hidden files can be left out of displayed values for the root UID and GID
by adding the -d option to the command line. This is useful when trying to match the numbers from
gfs2_quota with the results of a du command.

Examples

This example displays quota information for all users and groups that have a limit set or are using any
disk space on file system /mygfs2.

gfs2_quota list -f /mygfs2

This example displays quota information in sectors for group users on file system /mygfs2.

gfs2_quota get -g users -f /mygfs2 -s

3.5.3. Synchronizing Quotas

GFS2 stores all quota information in its own internal file on disk. A GFS2 node does not update this
quota file for every file system write; rather, it updates the quota file once every 60 seconds. This is
necessary to avoid contention among nodes writing to the quota file, which would cause a slowdown in
performance.

As a user or group approaches their quota limit, GFS2 dynamically reduces the time between
its quota-file updates to prevent the limit from being exceeded. The normal time period between
quota synchronizations is a tunable parameter, quota_quantum, and can be changed using the
gfs2_tool command. By default, the time period is 60 seconds. Also, the quota_quantum

Enabling/Disabling Quota Enforcement

19

parameter must be set on each node and each time the file system is mounted. (Changes to the
quota_quantum parameter are not persistent across unmounts.)

You can use the gfs2_quota sync command to synchronize the quota information from a node to
the on-disk quota file between the automatic updates performed by GFS2.

Usage

Synchronizing Quota Information

gfs2_quota sync -f MountPoint

MountPoint

Specifies the GFS2 file system to which the actions apply.

Tuning the Time Between Synchronizations

gfs2_tool settune MountPoint quota_quantum Seconds

MountPoint

Specifies the GFS2 file system to which the actions apply.

Seconds

Specifies the new time period between regular quota-file synchronizations by GFS2. Smaller
values may increase contention and slow down performance.

Examples

This example synchronizes the quota information from the node it is run on to file system /mygfs2.

gfs2_quota sync -f /mygfs2

This example changes the default time period between regular quota-file updates to one hour (3600
seconds) for file system /mygfs2 on a single node.

gfs2_tool settune /mygfs2 quota_quantum 3600

3.5.4. Enabling/Disabling Quota Enforcement

In GFS2 file systems, quota enforcement is disabled by default. To enable quota enforcement for a file
system, mount the file system with the quota=on option specified.

Usage

mount -o quota=on BlockDevice MountPoint

Chapter 3. Managing GFS2

20

To mount a file system with quota enforcement disabled, mount the file system with the quota=off
option specified. This is the default setting.

mount -o quota=off BlockDevice MountPoint

-o quota={on|off}

Specifies that quota enforcement is enabled or disabled when the file system is mounted.

BlockDevice

Specifies the block device where the GFS2 file system resides.

MountPoint

Specifies the directory where the GFS2 file system should be mounted.

Examples

In this example, the GFS2 file system on /dev/vg01/lvol0 is mounted on the /mygfs2 directory
with quota enforcement enabled.

mount -o quota=on /dev/vg01/lvol0 /mygfs2

3.5.5. Enabling Quota Accounting

It is possible to keep track of disk usage and maintain quota accounting for every user and
group without enforcing the limit and warn values. To do this, mount the file system with the
quota=account option specified.

Usage

mount -o quota=account BlockDevice MountPoint

-o quota=account

Specifies that user and group usage statistics are maintained by the file system, even though the
quota limits are not enforced.

BlockDevice

Specifies the block device where the GFS2 file system resides.

MountPoint

Specifies the directory where the GFS2 file system should be mounted.

Example

In this example, the GFS2 file system on /dev/vg01/lvol0 is mounted on the /mygfs2 directory
with quota accounting enabled.

mount -o quota=account /dev/vg01/lvol0 /mygfs2

Growing a File System

21

3.6. Growing a File System

The gfs2_grow command is used to expand a GFS2 file system after the device where the file
system resides has been expanded. Running a gfs2_grow command on an existing GFS2 file
system fills all spare space between the current end of the file system and the end of the device with a
newly initialized GFS2 file system extension. When the fill operation is completed, the resource index
for the file system is updated. All nodes in the cluster can then use the extra storage space that has
been added.

The gfs2_grow command must be run on a mounted file system, but only needs to be run on one
node in a cluster. All the other nodes sense that the expansion has occurred and automatically start
using the new space.

Note

Once you have created a GFS2 file system with the mkfs.gfs2 command, you cannot
decrease the size of the file system.

Usage

gfs2_grow MountPoint

MountPoint

Specifies the GFS2 file system to which the actions apply.

Comments

Before running the gfs2_grow command:

• Back up important data on the file system.

• Determine the volume that is used by the file system to be expanded by running a df MountPoint
command.

• Expand the underlying cluster volume with LVM. For information on administering LVM volumes,
see the LVM Administrator's Guide

After running the gfs2_grow command, run a df command to check that the new space is now
available in the file system.

Examples

In this example, the file system on the /mygfs2fs directory is expanded.

[root@dash-01 ~]# gfs2_grow /mygfs2fs
FS: Mount Point: /mygfs2fs
FS: Device: /dev/mapper/gfs2testvg-gfs2testlv
FS: Size: 524288 (0x80000)
FS: RG size: 65533 (0xfffd)
DEV: Size: 655360 (0xa0000)
The file system grew by 512MB.

Chapter 3. Managing GFS2

22

gfs2_grow complete.

Complete Usage

gfs2_grow [Options] {MountPoint | Device} [MountPoint | Device]

MountPoint

Specifies the directory where the GFS2 file system is mounted.

Device

Specifies the device node of the file system.

Table 3.3, “GFS2-specific Options Available While Expanding A File System” describes the GFS2-

specific options that can be used while expanding a GFS2 file system.

Option Description

-h Help. Displays a short usage message.

-q Quiet. Turns down the verbosity level.

-r MegaBytes Specifies the size of the new resource group. The default size is

256MB.

-T Test. Do all calculations, but do not write any data to the disk and do

not expand the file system.

-V Displays command version information.

Table 3.3. GFS2-specific Options Available While Expanding A File System

3.7. Adding Journals to a File System

The gfs2_jadd command is used to add journals to a GFS2 file system. You can add journals to
a GFS2 file system dynamically at any point without expanding the underlying logical volume. The
gfs2_jadd command must be run on a mounted file system, but it needs to be run on only one node
in the cluster. All the other nodes sense that the expansion has occurred.

Note

If a GFS2 file system is full, the gfs2_jadd will fail, even if the logical volume containing
the file system has been extended and is larger than the file system. This is because in
a GFS2 file system, journals are plain files rather than embedded metadata, so simply
extending the underlying logical volume will not provide space for the journals.

Before adding journals to a GFS file system, you can use the journals option of the gfs2_tool to
find out how many journals the GFS2 file system currently contains. The following example displays
the number and size of the journals in the file system mounted at /mnt/gfs2.

[root@roth-01 ../cluster/gfs2]# gfs2_tool journals /mnt/gfs2
journal2 - 128MB
journal1 - 128MB

Usage

23

journal0 - 128MB
3 journal(s) found.

Usage

gfs2_jadd -j Number MountPoint

Number

Specifies the number of new journals to be added.

MountPoint

Specifies the directory where the GFS2 file system is mounted.

Examples

In this example, one journal is added to the file system on the /mygfs2 directory.

gfs2_jadd -j1 /mygfs2

In this example, two journals are added to the file system on the /mygfs2 directory.

gfs2_jadd -j2 /mygfs2

Complete Usage

gfs2_jadd [Options] {MountPoint | Device} [MountPoint | Device]

MountPoint

Specifies the directory where the GFS2 file system is mounted.

Device

Specifies the device node of the file system.

Table 3.4, “GFS2-specific Options Available When Adding Journals” describes the GFS2-specific

options that can be used when adding journals to a GFS2 file system.

Flag Parameter Description

-h Help. Displays short usage message.

-J MegaBytes Specifies the size of the new journals in megabytes.

Default journal size is 128 megabytes. The minimum
size is 32 megabytes. To add journals of different sizes
to the file system, the gfs2_jadd command must be
run for each size journal. The size specified is rounded
down so that it is a multiple of the journal-segment size
that was specified when the file system was created.

Chapter 3. Managing GFS2

24

Flag Parameter Description

-j Number Specifies the number of new journals to be added by the
gfs2_jadd command. The default value is 1.

-q Quiet. Turns down the verbosity level.

-V Displays command version information.

Table 3.4. GFS2-specific Options Available When Adding Journals

3.8. Data Journaling

Ordinarily, GFS2 writes only metadata to its journal. File contents are subsequently written to disk by
the kernel's periodic sync that flushes file system buffers. An fsync() call on a file causes the file's
data to be written to disk immediately. The call returns when the disk reports that all data is safely
written.

Data journaling can result in a reduced fsync() time for very small files because the file data is
written to the journal in addition to the metadata. This advantage rapidly reduces as the file size
increases. Writing to medium and larger files will be much slower with data journaling turned on.

Applications that rely on fsync() to sync file data may see improved performance by using data
journaling. Data journaling can be enabled automatically for any GFS2 files created in a flagged
directory (and all its subdirectories). Existing files with zero length can also have data journaling turned
on or off.

Enabling data journaling on a directory sets the directory to "inherit jdata", which indicates that all files
and directories subsequently created in that directory are journaled. You can enable and disable data
journaling on a file with the chattr command.

The following commands enable data journaling on the /mnt/gfs2/gfs2_dir/newfile file and
then check whether the flag has been set properly.

[root@roth-01 ~]# chattr +j /mnt/gfs2/gfs2_dir/newfile
[root@roth-01 ~]# lsattr /mnt/gfs2/gfs2_dir

---------j--- /mnt/gfs2/gfs2_dir/newfile

The following commands disable data journaling on the /mnt/gfs2/gfs2_dir/newfile file and
then check whether the flag has been set properly.

[root@roth-01 ~]# chattr -j /mnt/gfs2/gfs2_dir/newfile
[root@roth-01 ~]# lsattr /mnt/gfs2/gfs2_dir

------------- /mnt/gfs2/gfs2_dir/newfile

You can also use the chattr command to set the j flag on a directory. When you set this flag for a
directory, all files and directories subsequently created in that directory are journaled. The following
set of commands sets the the j flag on the gfs2_dir directory, then checks whether the flag has
been set properly. After this, the commands create a new file called newfile in the /mnt/gfs2/
gfs2_dir directory and then check whether the j flag has been set for the file. Since the j flag is set
for the directory, then newfile should also have journaling enabled.

[root@roth-01 ~]# chattr -j /mnt/gfs2/gfs2_dir
[root@roth-01 ~]# lsattr /mnt/gfs2

Configuring atime Updates

25

---------j--- /mnt/gfs2/gfs2_dir
[root@roth-01 ~]# touch /mnt/gfs2/gfs2_dir/newfile
[root@roth-01 ~]# lsattr /mnt/gfs2/gfs2_dir

---------j--- /mnt/gfs2/gfs2_dir/newfile

3.9. Configuring atime Updates

Each file inode and directory inode has three time stamps associated with it:

• ctime — The last time the inode status was changed

• mtime — The last time the file (or directory) data was modified

• atime — The last time the file (or directory) data was accessed

If atime updates are enabled as they are by default on GFS2 and other Linux file systems then every
time a file is read, its inode needs to be updated.

Because few applications use the information provided by atime, those updates can require a
significant amount of unnecessary write traffic and file locking traffic. That traffic can degrade
performance; therefore, it may be preferable to turn off or reduce the frequency of atime updates.

Two methods of reducing the effects of atime updating are available:

• Mount with relatime (relative atime), which updates the atime if the previous atime update is
older than the mtime or ctime update.

• Mount with noatime, which disables atime updates on that file system.

3.9.1. Mount with relatime

The relatime (relative atime) Linux mount option can be specified when the file system is mounted.
This specifies that the atime is updated if the previous atime update is older than the mtime or
ctime update.

Usage

mount BlockDevice MountPoint -o relatime

BlockDevice

Specifies the block device where the GFS2 file system resides.

MountPoint

Specifies the directory where the GFS2 file system should be mounted.

Example

In this example, the GFS2 file system resides on the /dev/vg01/lvol0 and is mounted on directory
/mygfs2. The atime updates take place only if the previous atime update is older than the mtime
or ctime update.

mount /dev/vg01/lvol0 /mygfs2 -o relatime

Chapter 3. Managing GFS2

26

3.9.2. Mount with noatime

The noatime Linux mount option can be specified when the file system is mounted, which disables
atime updates on that file system.

Usage

mount BlockDevice MountPoint -o noatime

BlockDevice

Specifies the block device where the GFS2 file system resides.

MountPoint

Specifies the directory where the GFS2 file system should be mounted.

Example

In this example, the GFS2 file system resides on the /dev/vg01/lvol0 and is mounted on directory
/mygfs2 with atime updates turned off.

mount /dev/vg01/lvol0 /mygfs2 -o noatime

3.10. Suspending Activity on a File System

You can suspend write activity to a file system by using the gfs2_tool freeze command.
Suspending write activity allows hardware-based device snapshots to be used to capture the file
system in a consistent state. The gfs2_tool unfreeze command ends the suspension.

Usage

Start Suspension

gfs2_tool freeze MountPoint

End Suspension

gfs2_tool unfreeze MountPoint

MountPoint

Specifies the file system.

Examples

This example suspends writes to file system /mygfs2.

gfs2_tool freeze /mygfs2

This example ends suspension of writes to file system /mygfs2.

Repairing a File System

27

gfs2_tool unfreeze /mygfs2

3.11. Repairing a File System

When nodes fail with the file system mounted, file system journaling allows fast recovery. However,
if a storage device loses power or is physically disconnected, file system corruption may occur.
(Journaling cannot be used to recover from storage subsystem failures.) When that type of corruption
occurs, you can recover the GFS2 file system by using the fsck.gfs2 command.

Warning

The fsck.gfs2 command must be run only on a file system that is unmounted from all
nodes.

Note

If you have previous experience using the gfs_fsck command on GFS file systems, note
that the fsck.gfs2 command differs from some earlier releases of gfs_fsck in the in
the following ways:

• Pressing Ctrl+C while running the fsck.gfs2 interrupts processing and displays a

prompt asking whether you would like to abort the command, skip the rest of the current
pass, or continue processing.

• You can increase the level of verbosity by using the -v flag. Adding a second -v flag

increases the level again.

• You can decrease the level of verbosity by using the -q flag. Adding a second -q flag

decreases the level again.

• The -n option opens a file system as read-only and answers no to any queries

automatically. The option provides a way of trying the command to reveal errors without
actually allowing the fsck.gfs2 command to take effect.

Refer to the fsck.gfs2 man page for additional information about other command
options.

Running the fsck.gfs2 command requires system memory above and beyond the memory used
for the operating system and kernel. Each block of memory in the GFS2 file system itself requires
approximately five bits of additional memory, or 5/8 of a byte. So to estimate how many bytes of
memory you will need to run the fsck.gfs2 command on your file system, determine how many
blocks the file system contains and multiply that number by 5/8.

For example, to determine approximately how much memory is required to run the fsck.gfs2
command on a GFS2 file system that is 16TB with a block size of 4K, first determine how many blocks
of memory the file system contains by dividing 16Tb by 4K:

17592186044416 / 4096 = 4294967296

Chapter 3. Managing GFS2

28

Since this file system contains 4294967296 blocks, multiply that number by 5/8 to determine how
many bytes of memory are required:

4294967296 * 5/8 = 2684354560

This file system requires approximately 2.6GB of free memory to run the fsck.gfs2 command. Note
that if the block size was 1K, running the fsck.gfs2 command would require four times the memory,
or approximately 11GB.

Usage

fsck.gfs2 -y BlockDevice

-y
The -y flag causes all questions to be answered with yes. With the -y flag specified, the
fsck.gfs2 command does not prompt you for an answer before making changes.

BlockDevice

Specifies the block device where the GFS2 file system resides.

Example

In this example, the GFS2 file system residing on block device /dev/testvol/testlv is repaired.
All queries to repair are automatically answered with yes.

[root@dash-01 ~]# fsck.gfs2 -y /dev/testvg/testlv
Initializing fsck
Validating Resource Group index.
Level 1 RG check.
(level 1 passed)
Clearing journals (this may take a while)...
Journals cleared.
Starting pass1
Pass1 complete
Starting pass1b
Pass1b complete
Starting pass1c
Pass1c complete
Starting pass2
Pass2 complete
Starting pass3
Pass3 complete
Starting pass4
Pass4 complete
Starting pass5
Pass5 complete
Writing changes to disk
fsck.gfs2 complete

Bind Mounts and Context-Dependent Path Names

29

3.12. Bind Mounts and Context-Dependent Path Names

GFS2 file systems do not provide support for Context-Dependent Path Names (CDPNs), 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.

The bind option of the mount command allows you to remount part of a file hierarchy at a different
location while it is still available at the original location. The format of this command is as follows.

mount --bind olddir newdir

After executing this command, the contents of the olddir directory are available at two locations:
olddir and newdir. You can also use this option to make an individual file available at two

locations.

For example, after executing the following commands the contents of /root/tmp will be identical to
the contents of the previously mounted /var/log directory.

[root@menscryfa ~]# cd ~root
[root@menscryfa ~]# mkdir ./tmp
[root@menscryfa ~]# mount --bind /var/log /tmp

Alternately, you can use an entry in the /etc/fstab file to achieve the same results at mount time.
The following /etc/fstab entry will result in the contents of /root/tmp being identical to the
contents of the /var/log directory.

/var/log /root/tmp none bind 0 0

After you have mounted the file system, you can use the mount command to see that the file system
has been mounted, as in the following example.

[root@menscryfa ~]# mount | grep /tmp
/var/log on /root/tmp type none (rw,bind)

With a file system that supports Context-Dependent Path Names, you might have defined the /
bin directory as a Context-Dependent Path Name that would resolve to one of the following paths,

depending on the system architecture.

/usr/i386-bin
/usr/x86_64-bin
/usr/ppc64-bin

You can achieve this same functionality by creating an empty /bin directory. Then, using a script or
an entry in the /etc/fstab file, you can mount each of the individual architecture directories onto the
/bin directory with a mount -bind command. For example, you can use the following command as
a line in a script.

mount --bind /usr/i386-bin /bin

Chapter 3. Managing GFS2

30

Alternately, you can use the following entry in the /etc/fstab file.

/usr/1386-bin /bin none bind 0 0

A bind mount can provide greater flexibility than a Context-Dependent Path Name, since you can
use this feature to mount different directories according to any criteria you define (such as the value
of %fill for the file system). Context-Dependent Path Names are more limited in what they can
encompass. Note, however, that you will need to write your own script to mount according to a criteria
such as the value of %fill.

Warning

When you mount a file system with the bind option and the original file system was
mounted rw, the new file system will also be mounted rw even if you use the ro flag; the

ro flag is silently ignored. In this case, the new file system might be marked as ro in the /
proc/mounts directory, which may be misleading.

3.13. Bind Mounts and File System Mount Order

When you use the bind option of the mount command, you must be sure that the file systems are
mounted in the correct order. In the following example, the /var/log directory must be mounted
before executing the bind mount on the /tmp directory:

# mount --bind /var/log /tmp

The ordering of file system mounts is determined as follows:

• In general, file system mount order is determined by the order in which the file systems appear in

the fstab file. The exceptions to this ordering are file systems mounted with the _netdev flag or
filesystems that have their own init scripts.

• A file system with its own init script is mounted later in the initialization process, after the file

systems in the fstab file.

• File systems mounted with the _netdev flag are mounted when the network has been enabled on

the system.

If your configuration requires that you create a bind mount on which to mount a GFS2 file system, you
can order your fstab file as follows:

1. Mount local filesystems that are required for the bind mount.

2. Bind mount the directory on which to mount the GFS2 file system.

3. Mount the GFS2 file system.

If your configuration requires that you bind mount a local directory or file system onto a GFS2 file
system, listing the file systems in the correct order in the fstab file will not mount the file systems
correctly since the GFS2 file system will not be mounted until the GFS2 init script is run. In this
case, you should write an init script to execute the bind mount so that the bind mount will not take
place until after the GFS2 file system is mounted.

Bind Mounts and File System Mount Order

31

The following script is an example of a custom init script. This script performs a bind mount of two
directories onto two directories of a GFS2 filesystem. In this example, there is an existing GFS2 mount
point at /mnt/gfs2a, which is mounted when the GFS2 init script runs, after cluster startup.

In this example script, the values of the chkconfig statement indicate the following:

• 345 indicates the run levels that the script will be started in

• 29 is the start priority, which in this case indicates that the script will run at startup time after the

GFS2 init script, which has a start priority of 26

• 73 is the stop priority, which in this case indicates that the script will be stopped during shutdown
before the GFS2 script, which has a stop priority of 74

The start and stop values indicate that you can manually perform the indicated action by executing a
service start and a service stop command. For example, if the script is named fredwilma,
then you can execute service fredwilma start.

This script should be put in the /etc/init.d directory with the same permissions as the other scripts
in that directory. You can then execute a chkconfig on command to link the script to the indicated
run levels. For example, if the script is named fredwilma, then you can execute chkconfig
fredwilma on.

#!/bin/bash
#
# chkconfig: 345 29 73
# description: mount/unmount my custom bind mounts onto a gfs2 subdirectory
#
#
### BEGIN INIT INFO
# Provides:
### END INIT INFO

. /etc/init.d/functions
case "$1" in
start)
# In this example, fred and wilma want their home directories
# bind-mounted over the gfs2 directory /mnt/gfs2a, which has
# been mounted as /mnt/gfs2a
mkdir -p /mnt/gfs2a/home/fred &> /dev/null
mkdir -p /mnt/gfs2a/home/wilma &> /dev/null
/bin/mount --bind /mnt/gfs2a/home/fred /home/fred
/bin/mount --bind /mnt/gfs2a/home/wilma /home/wilma
;;

stop)
/bin/umount /mnt/gfs2a/home/fred
/bin/umount /mnt/gfs2a/home/wilma
;;

status)
;;

restart)
$0 stop
$0 start
;;

Chapter 3. Managing GFS2

32

reload)
$0 start
;;
*)
echo $"Usage: $0 {start|stop|restart|reload|status}"
exit 1
esac

exit 0

3.14. The GFS2 Withdraw Function

The GF2S withdraw function is a data integrity feature of GFS2 file systems in a cluster. If the GFS2
kernel module detects an inconsistency in a GFS2 file system following an I/O operation, the file
system becomes unavailable to the cluster. The I/O operation stops and the system waits for further
I/O operations to error out, preventing further damage. When this occurs, you can stop any other
services or applications manually, after which you can reboot and remount the GFS2 file system to
replay the journals. If the problem persists, you can unmount the file system from all nodes in the
cluster and perform file system recovery with the fsck.gfs2 command. The GFS withdraw function
is less severe than a kernel panic, which would cause another node to fence the node.

If your system is configured with the the gfs2 startup script enabled and the GFS2 file system is
included in the /etc/fstab file, the GFS2 file system will be remounted when you reboot. If the
GFS2 file system withdrew because of perceived file system corruption, it is recommended that you
run the fsck.gfs2 command before remounting the file system. In this case, in order to prevent your
file system from remounting at boot time, you can perform the following procedure:

1. Temporarily disable the startup script on the affected node with the following command:

# chkconfig gfs2 off

2. Reboot the affected node, starting the cluster software. The GFS2 file system will not be mounted.

3. Unmount the file system from every node in the cluster.

4. Run the fsck.gfs2 on the file system from one node only to ensure there is no file system

corruption.

5. Re-enable the startup script on the affected node by running the following command:

# chkconfig gfs2 on

6. Remount the GFS2 file system from all nodes in the cluster.

An example of an inconsistency that would yield a GFS2 withdraw is an incorrect block count. When
the GFS kernel deletes a file from a file system, it systematically removes all the data and metadata
blocks associated with that file. When it is done, it checks the block count. If the block count is not
one (meaning all that is left is the disk inode itself), that indicates a file system inconsistency since the
block count did not match the list of blocks found.

You can override the GFS2 withdraw function by mounting the file system with the -o
errors=panic option specified. When this option is specified, any errors that would normally

The GFS2 Withdraw Function

33

cause the system to withdraw cause the system to panic instead. This stops the node's cluster
communications, which causes the node to be fenced.

34

35

Appendix A. Converting a File System
from GFS to GFS2

Use the gfs2_convert command. To convert a GFS file system to a GFS2 file system.

Warning

If the conversion from GFS to GFS2 is interrupted by a power failure or any other issue,
restart the conversion tool. Do not attempt to execute the fsck.gfs2 command on the
file system until the conversion is complete.

1. Make a backup of your existing GFS file system.

2. Unmount the GFS file system from all nodes in the cluster.

3. Execute the gfs_fsck command on the GFS file system to ensure there is no file system

corruption and that you are working on a clean file system.

4. Execute gfs2_convert gfsfilesystem. The system will display warnings and confirmation

questions before converting gfsfilesystem to GFS2.

The following example converts a GFS filesystem on block device /dev/testvg/testlv to a GFS2
filesystem.

[root@dash-01 ~]# gfs2_convert /dev/testvg/testlv
gfs2_convert version 2 (built Sep 25 2007 12:41:29)
Copyright (C) Red Hat, Inc. 2004-2006 All rights reserved.

This program will convert a gfs1 filesystem to a gfs2 filesystem.
WARNING: This can't be undone. It is strongly advised that you:

1. Back up your entire filesystem first.

2. Run gfs_fsck first to ensure filesystem integrity.

3. Make sure the filesystem is NOT mounted from any node.

4. Make sure you have the latest software versions.

Convert /dev/testvg/testlv from GFS1 to GFS2? (y/n)y
Converting resource groups.
Converting inodes.
6 inodes converted.
Fixing file and directory information.
1 directories, 2 dirents fixed.
Converting journals.
Converting journal space to rg space.
Building system structures.
Removing obsolete gfs1 structures.
Committing changes to disk.
/dev/gfs2testvg/gfs2testlv: filesystem converted successfully to gfs2.
[root@dash-01 ~]#

36

37

Appendix B. Revision History

Revision 5.5-1 Thu Mar 11 2010 Steven Levine [e-mail]

Resolves: #546687
Documents features for the RHEL 5.5 release.

Resolves: #568179
Adds note clarifying support policy for single-node system.

Resolves: #562199
Adds note clairfying 16-node limitation.

Resolves: #515348
Documents new -o errors mount option.

Resolves: #573750
Documents memory requirements for fsck.gfs2.

Resolves: #574470
Clarifies issue of gfs2 requiring CLVM for Red Hat support.

Revision 5.4-1 Tue Aug 18 2009 Steven Levine [e-mail]

Resolves: #515807
Adds note clarifying that you cannot reduce the size of an existing file system.

Resolves: #480002
Adds caveat about unmounting a file system manually if you mounted it manually, adds section on
bind mounting a non-GFS2 file system to a GFS2 file system, adds sample custom init script.

Resolves: #458604
Adds section on GFS2 withdraw function.

Resolves: #498292
Clarifies documentation on adding journals.

Revision 1.0 Thu Jan 29 2009

38

39

Index

A

acl mount option, 12
adding journals to a file system, 22
atime, configuring updates, 25

mounting with noatime, 26
mounting with relatime, 25

audience, v

B

bind mount

mount order, 30

bind mounts, 29

C

configuration, before, 2
configuration, initial, 7

prerequisite tasks, 7

D

data journaling, 24

F

feedback, vi, vi
file system

adding journals, 22
atime, configuring updates, 25

mounting with noatime, 26

mounting with relatime, 25
bind mounts, 29
context-dependent path names (CDPNs), 29
data journaling, 24
growing, 21
making, 9
mount order, 30
mounting, 12, 15
quota management, 15

displaying quota limits, 17

enabling quota accounting, 20

enabling/disabling quota enforcement, 19

setting quotas, 16

synchronizing quotas, 18
repairing, 27
suspending activity, 26
unmounting, 15, 15

fsck.gfs2 command, 27

G

GFS2

atime, configuring updates, 25

mounting with noatime, 26

mounting with relatime, 25
managing, 9
quota management, 15

displaying quota limits, 17

enabling quota accounting, 20

enabling/disabling quota enforcement, 19

setting quotas, 16

synchronizing quotas, 18
withdraw function, 32

GFS2 file system maximum size, 1
GFS2-specific options for adding journals table,
23
GFS2-specific options for expanding file systems
table, 22
gfs2_grow command, 21
gfs2_jadd command, 22
gfs2_quota command, 16
growing a file system, 21

I

initial tasks

setup, initial, 7

introduction, v

audience, v

M

making a file system, 9
managing GFS2, 9
maximum size, GFS2 file system, 1
mkfs command, 9
mkfs.gfs2 command options table, 11
mount command, 12
mount table, 14
mounting a file system, 12, 15

O

overview, 1

configuration, before, 2

P

path names, context-dependent (CDPNs), 29
preface (see introduction)
prerequisite tasks

configuration, initial, 7

Index

40

Q

quota management, 15

displaying quota limits, 17
enabling quota accounting, 20
enabling/disabling quota enforcement, 19
setting quotas, 16

synchronizing quotas, 18
quota= mount option, 16
quota_quantum tunable parameter, 18

R

repairing a file system, 27

S

setup, initial

initial tasks, 7
suspending activity on a file system, 26
system hang at unmount, 15

T

tables

GFS2-specific options for adding journals, 23

GFS2-specific options for expanding file

systems, 22

mkfs.gfs2 command options, 11

mount options, 14

U

umount command, 15
unmount, system hang, 15
unmounting a file system, 15, 15

W

withdraw function, GFS2, 32