Diagram seems to imply an active/passive namenode setup like HDFS. Doesn't that limit it to tiny filesystems, and curse it with the same availability problems that plague HDFS?
"HopsFS is a new implementation of the Hadoop Filesystem (HDFS), that supports multiple stateless NameNodes, where the metadata is stored in MySQL Cluster, an in-memory distributed database. HopsFS enables more scalable clusters than Apache HDFS (up to ten times larger clusters), and enables NameNode metadata to be both customized and analyzed, because it can now be easily accessed via a SQL API."
There are other papers that describe HopsFS architecture in more details if you are interested: https://www.usenix.org/system/files/conference/fast17/fast17...