gfs2 (5)

Overview of the GFS2 filesystem

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.

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 gfs2_tool(8) utility's sb proto 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 gfs2_tool(8) utility's sb table 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.

GFS2 doesn't support errors=remount-ro or data=journal. It is not possible to switch support for user and group quotas on and off independently of each other. Some of the error messages are rather cryptic, if you encounter one of these messages check firstly that gfs_controld is running and secondly that you have enough journals on the filesystem for the number of nodes in use.

mount(8) for general mount options, chmod(1) and chmod(2) for access permission flags, acl(5) for access control lists, lvm(8) for volume management, ccs(7) for cluster management, umount(8), initrd(4).

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

gfs2_edit(8) A GFS2 debug tool (use with caution) fsck.gfs2(8) The GFS2 file system checker gfs2_grow(8) Growing a GFS2 file system gfs2_jadd(8) Adding a journal to a GFS2 file system mkfs.gfs2(8) Make a GFS2 file system gfs2_quota(8) Manipulate GFS2 disk quotas gfs2_tool(8) Tool to manipulate a GFS2 file system (obsolete) tunegfs2(8) Tool to manipulate GFS2 superblocks