gfs2

Section: File Formats (5)
Page Index

NAME

gfs2 - GFS2 reference guide

SYNOPSIS

Overview of the GFS2 filesystem

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:

mkfs.gfs2(8) Create a GFS2 filesystem
fsck.gfs2(8) The GFS2 filesystem checker
gfs2_grow(8) Growing a GFS2 filesystem
gfs2_jadd(8) Adding a journal to a GFS2 filesystem
tunegfs2(8) Tool to manipulate GFS2 superblocks
gfs2_edit(8) A GFS2 debug tool (use with caution)

MOUNT OPTIONS

lockproto=LockProtoName

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 LockProtoName must be one of the supported locking protocols, currently these are lock_nolock and lock_dlm.

The default lock protocol name is written to disk initially when creating the filesystem with mkfs.gfs2(8), -p option. It can be changed on-disk by using the tunegfs2(8) command.

The lockproto 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.

locktable=LockTableName

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 LockTableName is lock-module-specific. For lock_dlm, the format is clustername:fsname. For lock_nolock, the field is ignored.

The default cluster/filesystem name is written to disk initially when creating the filesystem with mkfs.gfs2(8), -t option. It can be changed on-disk by using the tunegfs2(8) command.

The locktable 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.

localflocks

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.

errors=[panic|withdraw]

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 debug option on kernel versions 2.6.31 and above.

acl

Enables POSIX Access Control List acl(5) support within GFS2.

spectator

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.

norecovery

A synonym for spectator

suiddir

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.

quota=[off/account/on]

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".

discard

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.

barrier

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)

commit=secs

This is similar to the ext3 commit= 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.

data=[ordered|writeback]

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.

meta

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.

quota_quantum=secs

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.

statfs_quantum=secs

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.

statfs_percent=value

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.

rgrplvb

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. Note: 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.

loccookie

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. Note: 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.

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.

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.

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.

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