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Global File System
GFS 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). GFS 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 GFS is perfect consistency -- changes made to the file system
on one machine show up immediately on all other machines in the cluster.
GFS uses interchangable inter-node locking mechanisms. Different lock
modules can plug into GFS and each file system selects the appropriate
lock module at mount time. Lock modules include:
lock_nolock -- 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/
In addition to interfacing with an external locking manager, a gfs lock
module is responsible for interacting with external cluster management
systems. Lock_dlm depends on user space cluster management systems found
at the URL above.
To use gfs 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
GFS2 is not on-disk compatible with previous versions of GFS.
The following man pages can be found at the URL above:
gfs2_fsck 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
mount.gfs2 to help mount(8) mount a filesystem
mkfs.gfs2 to make a filesystem