We published a tech brief that describes how extended attributes (xattrs) are used with the GlusterFS file system to manage a wide range of features:
Some xattrs are used to help GlusterFS improve performance or balance file storage. Others are used to determine how replication is done. Understanding how xattrs are used can give you insight into how Red Hat storage works.
Feel free to discuss any questions you have about GlusterFS xattrs here.