Database Reference
In-Depth Information
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Scalability
. Delivers information at near constant speed under load.
DOS prevention
. Prevents successful denial of service (DoS) attacks that would
otherwise prevent data availability.
In addition to ensuring redundancy of infrastructure components, you need to understand the
recovery objectives of your business to determine how to best implement your availability requirements.
SQL Azure offers a unique platform because all the areas just listed are automatically provided for.
SQL Azure offers a 99.9% availability guarantee through its service-level agreement (SLA). In order to
deliver this high availability, SQL Azure transparently keeps two additional standby databases for each
user database you create. If anything happens to one of your user databases, one of the two backups
takes over within a few seconds; you may not even notice the failover process. SQL Azure also provides
automatic handling of DoS attacks.
SQL Azure accomplishes failover using the architecture shown in Figure 4-1. You interact with a
proxy that directs your request to whichever of your databases is current. The standby databases aren't
accessible to you.
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Figure 4-1
. SQL Azure's standby database architecture
Note
In terms of availability, SQL Azure far surpasses SQL Server; SQL Azure is built on a scalable and highly
available platform that doesn't require configuration or tuning. None of the typical SQL Server configuration
settings are available in SQL Azure (such as CPU Affinity, Replication, Log Shipping, and so on).
Let's take an example of a project that needs to deploy a new application with high availability
requirements. The following items would need to be planned for in a traditional SQL Server installation
but are provided to you automatically with SQL Azure:
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Clustered SQL Server instance
. Install and configure Microsoft Cluster Service
and SQL Server instances in an active/active or active/passive configuration.
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RAID configuration
. Purchase new disks and hardware to install and configure a
RAID 10 (or RAID 0+1) disk array (for disk redundancy and performance).
