Global File System

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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