Questions about mgm node's role in the cluster

[shaunc]

Hi all,

My employer is in the planning phases of a High Availability upgrade to our server infrastructure. Among other things, we've been taking a look at MySQL Cluster. However, there are concerns in my department that the management node in the cluster - the one running ndb_mgmd - would introduce a single point of failure and negate the benefit of having the cluster. That can't be correct, but thus far I've been unable to gather enough information to explain why.

From the documentation and HOWTOs I've read, I understand that while it is recommended to keep ndb_mgmd running at all times, it is only _required_ to be running when the cluster's data nodes are started. This makes me somewhat unclear as to the management node's role in managing the cluster.

Suppose that the management node goes down (e.g. hardware failure); what happens? How does the cluster retain state information, stay synchronized, etc?

I am acting under the impression that ndb_mgmd is responsible for ensuring that the various data nodes are kept synchronized, and for routing queries from the SQL node to the appropriate data node. Am I way off base?

Thanks!