- Hot Failover: Clustering, Always On Availability Group (synchronous) - High Availabilty
- Warm Failover: Log shipping, Always On Availability Group (asynchronous) - disaster recovery
- Cold: unsynchronous
Always On Failover Clustering
Up to 64 servers. Always On Failover Clustered Instance. FCI. Single site. Shared storage. One server owns the FCI. Active node.
Windows Storage Replica (2016+) geoclusters
VIP is assigned to active instance. Application servers connect to VIP
- Active/Passive
- Active/Active - multiple instances in a cluster. Instances can move between nodes within a cluster.
Quorum may include a witness device
Authorative partition /fq
Quorum models:
- Node majority - odd number of nodes
- Node plus Disk Witness Majority
- Node plus file share witness majority - avoids VM issues with shared disk
Can change Node Weight to zero
Dynamic Quorum - Tie Breaker
Always On Availability Groups (AOAG)
AOAG = Database mirroring plus cluster - stand alone instances
Needs availability group listener installed on the cluster
AOAG - best for small database with low write profiles - allows for synchronous commits on all nodes (HA). Up to 8 replicas implies a 9 node cluster including 3 synchronous replicas
AOAG (DR) - asynchronous mode
Failover at level of AG. Multiple AG per instance. Maximum (100 database amd 10 AG) per instance (Microsoft recommendation)
One database mirroring and point per instance - all log streams go through this i/p
Each AG has its own network name and IP address
Application reconnects after failover
Automatic Page Repair
Good page gotten from a replica except - file header, database boot, allocation
Log Shipping
Backup transaction log on primary, ship to secondary; restore it
Recovery Modes
- recovery brings database online - not supported for log shipping
- norecovery keeps database offline to allow more backup to be applied - normal for log shipping
- standby bring database online as R/O
- can restore further backup
- TUF (Transaction Undo File)
Remote Monitor Server
- needs to be configured with log shipping
- cannot be added to an existing log shipping configuration
Failover - backup tail log; copy remaining backup; apply them in order; last one with RECOVERY
Can combine AOFOC with AOAG
- AOFOC HA
- AOAG DR and/or reporting
Synchronous mode allows automatic failover. Asynchronous mode only allows manual failover.
Can combine AOFOC with log shipping