InnoDB is the default storage engine for Cloud Databases. InnoDB enforces ACID transactions allowing for commit, rollback, and crash recovery capabilities to protect user data.
During a backup, a hot copy process is used on all tables. InnoDB tables record all transactions during the copy in order to replay them during a restore operation.
MyISAM tables are write-locked during the copy process in order to create a consistent backup. While the instance is being backed up you cannot add or delete databases, add or delete users, or delete, stop, or reboot the instance.
For more information about these engine types, see the MySQL documentation: