1. High Availability
   1. uninterrupted server uptime
   2. meet Service Level Agreements
   3. extra hardware: servers performing the same role
2. Sharepoint Roles
   1. Web Front End
      1. Network Load balancing
         1. Services: web servers, ftp, sp services
         2. Group of servers (cluster) run independently, dont share resources
         3. client requests are distributed
         4. increase network performance and availability, redundancy
         5. provided by software or hardware
   2. Application Servers
      1. Redundancy and load balancing
   3. Database Servers
      1. Failover clustering
         1. group of servers works together to provide services - applications
         2. if one servers fails, others continue providing servcies
         3. Technology in w2k8R2
         4. applications best suited (centralized data)
            1. SQL server
            2. exchange server
            3. file and print
            4. dns
         5. Benefits
            1. reduced downtime in event of server failure
            2. reduced downtime in event of OS failure
            3. reduced downtime during planned maintenance
            4. Topic
         6. cluster aware (applications and services): register with the failover cluster
      2. database (sql server) mirroring
         1. provides redundancy
         2. scope of protection: database
         3. In SP: mirorring provides redundancy for content, configuration and services databases
         4. high availability database mirorring capability (high safety mode with automatic failover)
         5. server instances
            1. principal
            2. witness
            3. mirror
         6. witness sends transactions directly from principal to mirror when transaction log buffer is written to disk
         7. ado.net connection object tries to connect to second connection string in the event the primary connection string cannot connect
         8. usually takes a few seconds
      3. Log shipping
         1. restores a full database backup of database on the primary server to secondary server
         2. applies transaction logs to the standby server
         3. available for user databases, not for system databases
         4. schedule log backups
         5. standby server can be used for read only queries (load balancing)
         6. no automatic failover: promote manually standby server to primary and reconfiger clients
         7. monitor server: logs problems with log shipping as well backups and restore operations
         8. combining mirorring and log shipping
            1. mirorring: one destination database
            2. log shipping: more than one destination database (alone or with mirorring)
            3. log shipping: delay restoring al log on the destination db. alone or with mirorring
      4. Database snapshots
      5. Read Only database
         1. set db to read only in sql
         2. sp recognizes and adjust the api
         3. only content db are read only
         4. sc are automatically set to read only