The SQL server ‘passive failover rule’ available under Volume Licensing, would commonly support situations when a primary server suffers a hardware or software failure (or is taken offline for routine maintenance or patch management) and requires the secondary ‘passive’ server to take over completely for ‘temporary’ support, but importantly, without requiring an additional licenses to be assigned to the secondary ‘passive’ server.
For example, common fail-over are included with SQL server, with support for basic high availability with 2 node fail-over clustering and a non-readable secondary instance, database backup log shopping, or database mirroring.
Under the legacy product-specific licensing terms for SQL server 2008, a standby server that is considered ‘passive’ (and not running any active workloads or reports) would generally not require an additional license to be assigned under Microsoft licensing (this includes back-up and restore related tasks under the passive designation), and would be covered under the licensed ‘active’ primary server.
Similarly, a secondary server, that would be utilized solely to maintain a copy of the database and will never take over from the primary does also fall under the ‘passive’ designation. However, the passive failover server rule will only support a single designated passive server under the allowance for each primary licensed server.
The SQL server ‘passive failover rule’ is an important licensing exception, and a principle driver of cost reduction in SQL licensing, but as Microsoft have sought to evolve their commercial licensing model to drive revenue growth, and incentivise customer purchasing behaviours to secure ongoing predictable revenue through their ‘Software Assurance’ maintenance model, the licensing has evolved incrementally since 2008 to curtail this licensing exception. This article charts the evolution of Software Assurance (SA) and the curtailment of the failover benefit to drive that revenue growth, and respond to emerging technologies.