The Always On availability groups feature is a high-availability and disaster-recovery solution that provides an enterprise-level alternative to database mirroring. Introduced in SQL Server 2012 (11.x), Always On availability groups maximizes the availability of a set of user databases for an enterprise. An availability group supports a failover environment for a discrete set of user databases, known as availability databases, that fail over together. An availability group supports a set of read-write primary databases and one to eight sets of corresponding secondary databases. Optionally, secondary databases can be made available for read-only access and/or some backup operations. Some customers prefer using secondary nodes for backup to reduce load on the primary node while some customers are OK with using primary node. To provide more flexibility for customers using Always On availability groups with Delphix Managed backups, delphix provides an option to choose backup policy during linking of dSource.
They can pick one of the following options that describe their backup policy as shown below.
Primary (default option): Backups are taken only on the primary node.
Secondary Only: Customers who never want to use primarily for their backups must choose this option as it ensures backups never go to the primary node. If the secondary nodes are down, the backups fail but do not use primary at all.
Secondary preferred: As the name suggests, one of the secondary nodes is used for backup. The backup will be taken on primary if none of the secondary nodes can be used for backup. So, customers who want reliable backups even if they are taken on the primary node if required should use this option.
The backup policy can be changed after dSource creation too as shown below.
The backup policy is not only provided during the linking phase of a dsource but also during the manual snapsync phase too to provide more flexibility to customers as shown below. The default option is the Backup Policy selected during the linking phase.