To achieve true high availability, you can set up Database Expert to acquire a license that is used in a three-server redundant configuration. The same license is served by all three license servers. With three-server redundancy, if any two of the three license servers are running (referred to as a quorum), the system is functional and serves its total complement of licenses.
Machines in a three-server redundant configuration must:
Run the same operating system
Communicate with each other
Reside on the same subnet
The three servers must be located physically close to each other. This form of redundancy requires that the servers exchange heartbeats periodically, and poor communication can cause poor performance. Avoid configuring redundant servers with slow communication or dial-up links.
Three-server redundancy provides only hardware failover protection and does not provide load-balancing because only one of the three servers is “master,” capable of issuing licenses. Because all clients must contact the “master,” all clients must have reliable networking to a single machine. To implement load-balancing, see “Setting up multiple network servers”.
Because Sybase provides grace periods for any licensing
issues, setting up the license servers for failover may be unnecessary. Database Expert operations
are not compromised as long as license server issues are fixed within
the grace period.
