The Global File System is part of Redhat's Linux Cluster. 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 filesystem, but also uses a lock module to allow the computers coordinate their I/O so filesystem consistency is maintained. One of the nifty features of GFS is perfect consistency; changes made to the filesystem on one machine show up immediately on all other machines in the cluster.