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gfs2 - GFS2 reference guide
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
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.
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
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
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
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
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.
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.
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
acl Enables POSIX Access Control List acl(5) support within GFS2.
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.
A synonym for spectator
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.
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".
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.
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)
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.
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.
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.
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.
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