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Microsoft is changing the way it sells Azure SQL Database. The new subscription model offers three service tiers: Basic, Standard and Premium. The purpose of the new tier system is to deliver more predictable performance, simplify billing and avoid costly workarounds. Microsoft plans to retire the existing service tiers, Web and Business, in April 2015.
The new data tiers are currently offered as preview editions. They distinguish themselves from one another primarily by database size, performance level, disaster recovery capabilities and price. Microsoft is offering the preview editions at half of their anticipated cost at general availability (GA). Subscribers are charged per day for the number of databases they used that day. Price per database is calculated based on the highest service tier and performance level used that day. All three new service tiers come with a service-level agreement of 99.95% uptime.
Azure SQL Database service tiers
The entry-level edition is the Basic service tier. It caters to applications with light transactional loads and relatively small data sets. Databases at this tier are limited to a maximum size of 2 GB and cost about $3 per month at the preview rate. Performance objectives for the Basic tier are based on a predictable per-hour transaction rate, which the Azure SQL Database Benchmark (ASDB) puts at 17,805 transactions per hour for a typical online transaction processing (OLTP) application.
The Standard edition is the Intermediate service tier, and a good place to start if you're supporting cloud-based business applications that need more size and performance than the Basic tier can offer. The subscription rate for a single database is either $20 or $100 per month with the preview rate, depending on the selected performance level. The Standard edition supports databases as large as 250 GB. Unlike the Basic service, the Standard tier aims to deliver a predictable per-minute transaction rate, which the ASDB reports as either 782 or 2,954 transactions per minute, depending on the performance level.
The top-of-the-line service tier is the Premium edition. The Premium service tier is best for mission-critical applications that require high performance levels and advanced disaster recovery features. It supports databases as large as 500 GB and costs between $465 and $3,720 per month at the preview rate, with a performance goal based on a predictable per-second transaction rate. The ASDB cites a performance rate of 98, 192 or 730 transactions per second, depending on the performance level.
Azure SQL Database performance levels
At the heart of the new service tier model is the performance level. The Basic tier offers only one performance level, while the Standard and Premium tiers offer multiple performance levels. The higher the performance level, the greater the workload a database can support. Performance levels are based on the Database Throughput Unit (DTU). A DTU is a performance measurement that takes into account the CPU and memory and I/O resources available to the database engine. The higher the number of DTUs, the greater the workloads a database can support.
As you step up the service tier ladder, each performance level offers an increasing number of DTUs. For example, the performance level available to the Basic service provides five DTUs of workload capacity. The Standard service offers two performance levels, one that provides 20 DTUs of workload power and one that provides 50 DTUs. The Premium service tier supports three performance levels. The first provides 100 DTUs; the second, 200 DTUs; and the third, 800 DTUs.
Azure SQL Database business continuity
The new service tiers also introduce business continuity, a set of disaster recovery features. The Geo-Replication data protection and disaster recovery option is one of the business continuity feature introduced with the new service tiers. The Standard and Premium tiers both provide Standard Geo-Replication, which lets you create a single offline secondary copy of your database in a different region than your primary. In addition, the Premium tier supports Active Geo-Replication. Active Geo-Replication creates multiple readable secondary databases across regions. You can use the secondary databases for database migration, to support read-only workloads or to act as failover backups. You can also select the regions where your secondary databases are housed as the control when failover occurs.
One feature, Point in Time Restore, takes advantage of Azure's automatic backup of your databases to geo-replicated storage. Point in Time Restore lets you restore a database from an Azure backup in geo-replicated storage. Although each service tier supports this feature, the length of time that backups are maintained varies from one tier to the next. With Basic, you get seven days of backups. Standard provides 14 days and Premium 35 days.
The Database Copy feature in SQL Database is also available to all three service tiers. This feature creates a copy of a database, which can be on the same server as the original database or on a different server, and in the same region as the original or in a different region. When the copy operation is complete, the new database is transactionally consistent with the original. All three service tiers let you use the SQL Database Export service to export a Backup Package (BACPAC) file from your database in order to create a copy elsewhere.
Out with the old, in with the new
Microsoft currently plans to retire the Web and Business tiers on April 24, 2015. However, the company has promised to give customers at least six months to transition off the Web and Business editions after the new data tiers become generally available, even if that means pushing out the retirement date. Microsoft has not yet disclosed when the three new service tiers will hit GA.
Since the new data tiers are in preview, the services are still being fine-tuned and adjusted in response to user feedback. Currently, subscribers cannot upgrade a Web or Business database to the Basic or Standard tier, although they can export the database via a BACPAC file. Microsoft plans to remove this limitation by the time the new tiers are ready for GA. However, not all Web and Business features will be available in the new tiers, the most notable missing feature being federations.
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