Global File System
------------------

http://sources.redhat.com/cluster/

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 interchangable inter-node locking mechanisms. The currently
supported methods are:

  lock_nolock -- does no real locking and allows gfs to be used as a
  local file system

  lock_dlm -- uses a 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:

  $ gfs2_mkfs -p lock_nolock -j 1 /dev/block_device
  $ mount -t gfs2 /dev/block_device /dir

GFS2 is not on-disk compatible with previous versions of GFS, but it does
use a very smilar on-disk format, so that upgrading a filesystem can be
done in place and makes relatively few changes. Upgrading a filesystem
to GFS2 is not currently reversible.

The following man pages can be found at the URL above:
  mkfs.gfs2	to make a filesystem
  fsck.gfs2	to repair a filesystem
  gfs2_grow	to expand a filesystem online
  gfs2_jadd	to add journals to a filesystem online
  gfs2_tool	to manipulate, examine and tune a filesystem
  gfs2_quota	to examine and change quota values in a filesystem
  gfs2_convert	to convert a gfs filesystem to gfs2
  mount.gfs2	to find mount options