Check out RonDB (https://www.rondb.com/blog) which is a fork of MySQL Cluster but has support for elasticity with no downtime, backups, etc.
Disclaimer: i am involved with RonDB.
No. It's a distributed database. Transactions are committed in memory, and then (by default every second) committed as a group to disk. This gives you phenomenal write throughput and low latency, but the tradeoff is that if a whole cluster goes lights out, you could lose a second of data. It's kind of like turning off fsync for InnoDB.