Designing a highly availabile directory service

Make copies, the key idea of the chapter. Admins have to deal with various situations to safely replicate data and recover them when needed. A significant difference is that possible failures are analyzed extensively, like node failure and link failure. It's complex and difficult to ensure things keep working when multiple failures happen. So we need more replicas to ensure availability. Also the read performance is critical for performance evaluation, so sample topologies are optimized for read performance. The 3 roles: master, hub and consumer help clarifying the situation and improving efficiency.