.. SPDX-License-Identifier: GPL-2.0

====================
Global File System 2
====================

Overview
========

GFS2 is a cluster file system. It allows a cluster of computers to
simultaneously use a block device that is shared between them (with FC,
iSCSI, NBD, etc).  GFS2 reads and writes to the block device like a local
file system, but also uses a lock module to allow the computers coordinate
their I/O so file system consistency is maintained.  One of the nifty
features of GFS2 is perfect consistency -- changes made to the file system
on one machine show up immediately on all other machines in the cluster.

GFS2 uses interchangeable inter-node locking mechanisms, the currently
supported mechanisms are:

  lock_nolock
    - allows GFS2 to be used as a local file system

  lock_dlm
    - uses the distributed lock manager (dlm) for inter-node locking.
      The dlm is found at linux/fs/dlm/

lock_dlm depends on user space cluster management systems found
at the URL above.

To use GFS2 as a local file system, no external clustering systems are
needed, simply::

  $ mkfs -t gfs2 -p lock_nolock -j 1 /dev/block_device
  $ mount -t gfs2 /dev/block_device /dir

The gfs2-utils package is required on all cluster nodes and, for lock_dlm, you
will also need the dlm and corosync user space utilities configured as per the
documentation.

gfs2-utils can be found at https://pagure.io/gfs2-utils

GFS2 is not on-disk compatible with previous versions of GFS, but it
is pretty close.

The following man pages are available from gfs2-utils:

  ============		=============================================
  fsck.gfs2		to repair a filesystem
  gfs2_grow		to expand a filesystem online
  gfs2_jadd		to add journals to a filesystem online
  tunegfs2		to manipulate, examine and tune a filesystem
  gfs2_convert		to convert a gfs filesystem to GFS2 in-place
  mkfs.gfs2		to make a filesystem
  ============		=============================================

Implementation Notes
====================

.. toctree::
   :maxdepth: 1

   glocks
   uevents
