Interesting approach. Google colossus file system also stores the metadata in a high performance key value store.

But their key-value store is not transactional. Afaik, they don't define the semantics of operations like 'mv' across cells. Higher level frameworks like Spanner/BigTable work around that limitation - but are forced to present data in tabular format. HopsFS allows to to treat them as files.

Disclaimer: i'm a co-author.