- By Victor Isakov
High availability is not equivalent to disaster recovery.
Log Shipping is not a high availability technology.
Log Shipping supports multiple secondary servers.
With Log Shipping, users cannot access the secondary database when a log backup is being restored.
Failover clustering and Availability Groups rely on the Windows Server Failover Cluster (WSFC) feature.
Failover clustering and Availability Groups support automatic failover.
The scope of protection in Availability Groups is at the database level.
Availability Groups support three failover partners with SQL Server 2016.
Each replica in an Availability Group maintains its own version of the database.
Availability Groups support asynchronous and synchronous communication between the replicas.
With an Availability Groups you can only perform a manual fail over to a synchronous replica.
A forced failover in an Availability Group to an asynchronous replica can result in data loss.
Availability Groups support readable secondaries.
Availability Groups are the only high-availability technology that allows you to scale out your database solution.
You can offload reports, read operations, database consistency checks and backup operations to a readable secondary.
SQL Server 2016 Standard Edition supports Basic Availability Groups, which is intended to replace Database Mirroring.
Distributed Availability Groups are designed to be used between data centers where you want to minimize the network usage across the WAN link between your data centers.
SQL Server 2016 provides limited support for DTC in Availability Groups.
Availability Groups are more complicated to maintain and administer as they do not automatically synchronize logins, SQL Server Agent jobs and other external database dependencies between replicas.
You can install a number of SQL Server Failover cluster instances on a Windows failover cluster.
The scope of protection in a failover cluster is at the instance level.
WSFC no longer require a domain.
Failover clustering uses shared storage which represents a single point of failure.
Failover clustering will work with SMB 3.0 file shares as a location for your database files.
Cluster Shared Volumes (CSVs) represent a new clustered file system in Windows Server.
SQL Server 2014 added support for (CSVs).
CSV remove the dependency on physical disks, which reduces the fail over time in a failover cluster.