GlusterFS is a clustered file system that can be used when you want to share the content across different machines which can be accomplished by NFS as well. But the difference is, NFS failover is hard.
In GlusterFS, you can add two servers known as bricks in Gluster’s terminology on which your volume can be created as a replica. All data is replicated to both the servers by Gluster. GlusterFS has support for advertising the volumes as NFS shares as well, but I didn’t use it because of the basic reason – failover.