News

Microsoft: Updated Azure SQL Database SLA Is Industry Best

• By Kurt Mackie
• August 01, 2019

Microsoft's new service-level agreement (SLA) for Azure SQL Database offers the most guaranteed uptime compared to its competitors, the company claimed this week.

The new SLA adds uptime perks for organizations that use the "Business Critical" tier. If organizations use zone-redundant databases with the Azure SQL Database service under the Business Critical tier (also known as "Premium"), then they can now be eligible for a 99.995 percent SLA.

The 99.995 percent SLA amounts to an estimated 26.28 minutes of downtime per year. That figure is about half the usual 99.99 percent SLA downtime assurance of 52.56 minutes per year, according to a Wednesday announcement by Alexander Nosov, a principal program manager for Azure SQL Database.

Nosov admitted that 26 minutes of downtime per year "may not be acceptable" for some organizations' applications. However, he suggested that increased availability could be enabled by "combining a zone redundant database configuration with a business continuity design."

The Business Critical tier of Azure SQL Database is designed for use with "the most demanding applications," Nosov explained. It involves using "Gen 5" logical CPUs, which are based on Intel Broadwell 2.3 GHz processors, as described at the Azure SQL Database pricing page.

Nosov claimed that the new 99.995 percent SLA "is the highest SLA in the industry among all relational database services." The announcement included a table comparing Azure SQL Database's uptime guarantees favorably against the guarantees described for the Amazon Web Services Relational Database Service, Google Cloud Platform Cloud SQL service, along with Alibaba and Oracle Cloud offerings.

There's also a so-called "business continuity SLA" addition for organizations opting to use georeplication with the Azure SQL Database service. Here's how Nosov explained it:

We offer a business continuity SLA for databases in the business critical tier that are geo-replicated between two different Azure regions. That SLA comes with very strong guarantees of a five second recovery point objective (RPO) and a 30 second recovery time objective (RTO), including a 100% monthly cost credit when the SLA is not maintained. Azure SQL Database is the only relational database service in the industry offering a business continuity SLA.

With georeplication, Microsoft maintains database replicas "in two or more geographically separated locations" on Azure SQL Database infrastructure. This arrangement is used to avoid network latency performance hits, Nosov explained. He admitted that asynchronous replication is used with this georeplication approach, which has "the potential for data loss" for organizations, but Nosov claimed it still supports "very aggressive guarantees." That's apparently a reference to Microsoft's RPO and RTO guarantees.

Here's that scenario, as outlined by Nosov:

Recovery time objective (RTO) measures how quickly the availability of the application can be restored. Recovery point objective (RPO) measures the maximum expected data loss after the availability is restored. Not only do we provide SLAs of five seconds for RPO and 30 seconds for RTO, but we also offer an industry first, 100% service credit if these SLAs are not met. That means if any of your database failover requests do not complete within 30 seconds or any time the replication lag exceeds five seconds in 99th percentile within an hour, you are eligible for a service credit for 100% of the monthly cost of the secondary database in question.

These SLAs are only applicable if an organization has a volume licensing agreement in place with Microsoft. Organization have to submit a downtime claim to Microsoft support, and they'll only get a service credit if the claim gets approved. Microsoft's assessment process can take up to 45 days. The service credit is just 10 percent for organizations with the "four-nines" SLAs, according to tables in Microsoft's SLA document.

Microsoft defines a service credit as "the percentage of the Applicable Monthly Service Fees credited to you following Microsoft's claim approval."