Ask HS: Design and Implementation of scalable services?

We have written agents deployed/distributed across the network. Agents sends data every 15 Secs may be even 5 secs. Working on a service/system to which all agent can post data/tuples with marginal payload. Upto 5% drop rate is acceptable. Ultimately the data will be segregated and stored into DBMS System (currently we are using MSQL).

Question(s) I am looking for answer

1. Client/Server Communication: Agent(s) can post data. Status of sending data is not that important. But there is a remote where Agent(s) to be notified if the server side system generates an event based on the data sent.

- Lot of advices from internet suggests using Message Bus (ActiveMQ) for async communication. Multicast and UDP are the alternatives.

2. Persistence: After some evaluation data to be stored in DBMS System.

- End of processing data is an aggregated record for which MySql looks scalable. But on the volume of data is exponential. Considering HBase as an option.

Looking if there are any alternatives for above two scenarios and get expert advice.