.TH gfs2 5

.SH NAME

gfs2 \- GFS2 reference guide

.SH SYNOPSIS

Overview of the GFS2 filesystem

.SH DESCRIPTION

GFS2 is a clustered filesystem, designed for sharing data between 

multiple nodes

connected to a common shared storage device. It can also be used as a

local filesystem on a single node, however since the design is aimed

at clusters, that will usually result in lower performance than using

a filesystem designed specifically for single node use.

GFS2 is a journaling filesystem and one journal is required for each node

that will mount the filesystem. The one exception to that is spectator

mounts which are equivalent to mounting a read-only block device and as

such can neither recover a journal or write to the filesystem, so do not

require a journal assigned to them.

The GFS2 documentation has been split into a number of sections:

\fBmkfs.gfs2\fP(8) Create a GFS2 filesystem

.br

\fBfsck.gfs2\fP(8) The GFS2 filesystem checker

.br

\fBgfs2_grow\fP(8) Growing a GFS2 filesystem

.br

\fBgfs2_jadd\fP(8) Adding a journal to a GFS2 filesystem

.br

\fBtunegfs2\fP(8) Tool to manipulate GFS2 superblocks

.br

\fBgfs2_edit\fP(8) A GFS2 debug tool (use with caution)

.SH MOUNT OPTIONS

.TP

\fBlockproto=\fP\fILockProtoName\fR

This specifies which inter-node lock protocol is used by the GFS2 filesystem

for this mount, overriding the default lock protocol name stored in the

filesystem's on-disk superblock.

The \fILockProtoName\fR must be one of the supported locking protocols,

currently these are \fIlock_nolock\fR and \fIlock_dlm\fR.

The default lock protocol name is written to disk initially when creating the

filesystem with \fBmkfs.gfs2\fP(8), -p option.  It can be changed on-disk by

using the \fBtunegfs2\fP(8) command.

The \fBlockproto\fP mount option should be used only under special

circumstances in which you want to temporarily use a different lock protocol

without changing the on-disk default. Using the incorrect lock protocol

on a cluster filesystem mounted from more than one node will almost

certainly result in filesystem corruption.

.TP

\fBlocktable=\fP\fILockTableName\fR

This specifies the identity of the cluster and of the filesystem for this

mount, overriding the default cluster/filesystem identify stored in the

filesystem's on-disk superblock.  The cluster/filesystem name is recognized

globally throughout the cluster, and establishes a unique namespace for

the inter-node locking system, enabling the mounting of multiple GFS2

filesystems.

The format of \fILockTableName\fR is lock-module-specific.  For

\fIlock_dlm\fR, the format is \fIclustername:fsname\fR.  For

\fIlock_nolock\fR, the field is ignored.

The default cluster/filesystem name is written to disk initially when creating

the filesystem with \fBmkfs.gfs2\fP(8), -t option.  It can be changed on-disk

by using the \fBtunegfs2\fP(8) command.

The \fBlocktable\fP mount option should be used only under special

circumstances in which you want to mount the filesystem in a different cluster,

or mount it as a different filesystem name, without changing the on-disk

default.

.TP

\fBlocalflocks\fP

This flag tells GFS2 that it is running as a local (not clustered) filesystem,

so it can allow the kernel VFS layer to do all flock and fcntl file locking.

When running in cluster mode, these file locks require inter-node locks,

and require the support of GFS2.  When running locally, better performance

is achieved by letting VFS handle the whole job.

This is turned on automatically by the lock_nolock module.

.TP

\fBerrors=\fP\fI[panic|withdraw]\fR

Setting errors=panic causes GFS2 to oops when encountering an error that

would otherwise cause the

mount to withdraw or print an assertion warning. The default setting

is errors=withdraw. This option should not be used in a production system.

It replaces the earlier \fBdebug\fP option on kernel versions 2.6.31 and

above.

.TP

\fBacl\fP

Enables POSIX Access Control List \fBacl\fP(5) support within GFS2.

.TP

\fBspectator\fP

Mount this filesystem using a special form of read-only mount.  The mount

does not use one of the filesystem's journals. The node is unable to

recover journals for other nodes.

.TP

\fBnorecovery\fP

A synonym for spectator

.TP

\fBsuiddir\fP

Sets owner of any newly created file or directory to be that of parent

directory, if parent directory has S_ISUID permission attribute bit set.

Sets S_ISUID in any new directory, if its parent directory's S_ISUID is set.

Strips all execution bits on a new file, if parent directory owner is different

from owner of process creating the file.  Set this option only if you know

why you are setting it.

.TP

\fBquota=\fP\fI[off/account/on]\fR

Turns quotas on or off for a filesystem.  Setting the quotas to be in

the "account" state causes the per UID/GID usage statistics to be

correctly maintained by the filesystem, limit and warn values are

ignored.  The default value is "off".

.TP

\fBdiscard\fP

Causes GFS2 to generate "discard" I/O requests for blocks which have

been freed. These can be used by suitable hardware to implement

thin-provisioning and similar schemes. This feature is supported

in kernel version 2.6.30 and above.

.TP

\fBbarrier\fP

This option, which defaults to on, causes GFS2 to send I/O barriers

when flushing the journal. The option is automatically turned off

if the underlying device does not support I/O barriers. We highly

recommend the use of I/O barriers with GFS2 at all times unless

the block device is designed so that it cannot lose its write cache

content (e.g. its on a UPS, or it doesn't have a write cache)

.TP

\fBcommit=\fP\fIsecs\fR

This is similar to the ext3 \fBcommit=\fP option in that it sets

the maximum number of seconds between journal commits if there is

dirty data in the journal. The default is 60 seconds. This option

is only provided in kernel versions 2.6.31 and above.

.TP

\fBdata=\fP\fI[ordered|writeback]\fR

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.  Data=writeback mode writes the user data to the disk

at any time after it's dirtied.  This doesn't provide the same

consistency guarantee as ordered mode, but it should be slightly

faster for some workloads.  The default is ordered mode.

.TP

\fBmeta\fP

This option results in selecting the meta filesystem root rather than

the normal filesystem root. This option is normally only used by

the GFS2 utility functions. Altering any file on the GFS2 meta filesystem

may render the filesystem unusable, so only experts in the GFS2

on-disk layout should use this option.

.TP

\fBquota_quantum=\fP\fIsecs\fR

This sets the number of seconds for which a change in the quota

information may sit on one node before being written to the quota

file. This is the preferred way to set this parameter. The value

is an integer number of seconds greater than zero. The default is

60 seconds. Shorter settings result in faster updates of the lazy

quota information and less likelihood of someone exceeding their

quota. Longer settings make filesystem operations involving quotas

faster and more efficient.

.TP

\fBstatfs_quantum=\fP\fIsecs\fR

Setting statfs_quantum to 0 is the preferred way to set the slow version

of statfs. The default value is 30 secs which sets the maximum time

period before statfs changes will be syned to the master statfs file.

This can be adjusted to allow for faster, less accurate statfs values

or slower more accurate values. When set to 0, statfs will always

report the true values.

.TP

\fBstatfs_percent=\fP\fIvalue\fR

This setting provides a bound on the maximum percentage change in

the statfs information on a local basis before it is synced back

to the master statfs file, even if the time period has not

expired. If the setting of statfs_quantum is 0, then this setting

is ignored.

.TP

\fBrgrplvb\fP

This flag tells gfs2 to look for information about a resource group's free

space and unlinked inodes in its glock lock value block. This keeps gfs2 from

having to read in the resource group data from disk, speeding up allocations in

some cases.  This option was added in the 3.6 Linux kernel. Prior to this

kernel, no information was saved to the resource group lvb. \fBNote:\fP To

safely turn on this option, all nodes mounting the filesystem must be running

at least a 3.6 Linux kernel. If any nodes had previously mounted the filesystem

using older kernels, the filesystem must be unmounted on all nodes before it

can be mounted with this option enabled. This option does not need to be

enabled on all nodes using a filesystem.

.TP

\fBloccookie\fP

This flag tells gfs2 to use location based readdir cookies, instead of its

usual filename hash readdir cookies.  The filename hash cookies are not

guaranteed to be unique, and as the number of files in a directory increases,

so does the likelihood of a collision.  NFS requires readdir cookies to be

unique, which can cause problems with very large directories (over 100,000

files). With this flag set, gfs2 will try to give out location based cookies.

Since the cookie is 31 bits, gfs2 will eventually run out of unique cookies,

and will fail back to using hash cookies. The maximum number of files that

could have unique location cookies assuming perfectly even hashing and names of

8 or fewer characters is 1,073,741,824. An average directory should be able to

give out well over half a billion location based cookies. This option was added

in the 4.5 Linux kernel. Prior to this kernel, gfs2 did not add directory

entries in a way that allowed it to use location based readdir cookies.

\fBNote:\fP To safely turn on this option, all nodes mounting the filesystem

must be running at least a 4.5 Linux kernel. If this option is only enabled on

some of the nodes mounting a filesystem, the cookies returned by nodes using

this option will not be valid on nodes that are not using this option, and vice

versa.  Finally, when first enabling this option on a filesystem that had been

previously mounted without it, you must make sure that there are no outstanding

cookies being cached by other software, such as NFS.

.SH SETUP

GFS2 clustering is driven by the dlm, which depends on dlm_controld to provide

clustering from userspace.  dlm_controld clustering is built on corosync

cluster/group membership and messaging. GFS2 also requires clustered lvm which

is provided by lvmlockd or, previously, clvmd. Refer to the documentation for

each of these components and ensure that they are configured before setting up

a GFS2 filesystem. Also refer to your distribution's documentation for any

specific support requirements.

Ensure that gfs2-utils is installed on all nodes which mount the filesystem as

it provides scripts required for correct withdraw event response.

.B 1. Create the gfs2 filesystem

mkfs.gfs2 -p lock_dlm -t cluster_name:fs_name -j num /path/to/storage

The cluster_name must match the name configured in corosync (and thus dlm).

The fs_name must be a unique name for the filesystem in the cluster.

The -j option is the number of journals to create; there must

be one for each node that will mount the filesystem.

.PP

.B 2. Mount the gfs2 filesystem

If you are using a clustered resource manager, see its documentation for

enabling a gfs2 filesystem resource. Otherwise, run:

mount /path/to/storage /mountpoint

Run "dlm_tool ls" to verify the nodes that have each fs mounted.

.PP

.B 3. Shut down

If you are using a clustered resource manager, see its documentation for

disabling a gfs2 filesystem resource. Otherwise, run:

umount -a -t gfs2

.PP

.SH SEE ALSO

\fBmount\fP(8) and \fBumount\fP(8) for general mount information,

\fBchmod\fP(1) and \fBchmod\fP(2) for access permission flags,

\fBacl\fP(5) for access control lists,

\fBlvm\fP(8) for volume management,

\fBdlm_controld\fP(8),

\fBdlm_tool\fP(8),

\fBdlm.conf\fP(5),

\fBcorosync\fP(8),

\fBcorosync.conf\fP(5),