Safeguarding Confidential Data in SharePoint 2010 : Outlining Database Mirroring Requirements

3/25/2011 9:00:59 AM
The following requirements apply to a SQL Database mirroring environment.

Examining Supported SQL Server Editions

SharePoint 2010 supports SQL Server 2005, SQL Server 2008, and SQL Server 2008 R2. However, if planning for database mirroring, it is strongly recommended to deploy a version of SQL Server 2008 or SQL Server 2008 R2 to take advantage of the core performance enhancements for database mirroring. One of these major enhancements includes the ability to compress the stream of log records from the principal server to the mirror server, resulting in a sizable performance increase.

Table 1 lists the available database mirroring features within the supported versions of SQL Server 2005 and SQL Server 2008.

Table 1. Available Database Mirroring Features in SQL Server 2005 and SQL Server 2008
Database Mirroring FeatureEnterprise EditionStandard EditionWorkgroup EditionExpress Edition
Synchronous modeYesYesNoNo
Asynchronous modeYesNoNoNo


Although the witness server can run Workgroup or Express edition of SQL Server, both the principal and mirror servers must be running the same version of SQL Server. To ensure proper business continuity, it is also recommended to have both the principal and mirror servers running on similar hardware, if not identical.

Considering Security Requirements

There are two types of authentication for a database mirroring session: Windows Authentication (NTLM or Kerberos) or certificates. After a database mirroring session is initialized, the principal server sends a load of transaction logs to the mirror server using TCP. In addition to transporting log files between the two partners in a database mirroring session, TCP is used by the witness server to monitor the state of the two partners and determine when an automatic failover is necessary. In fact, all communication between the principal server, the mirror server, and the witness server (if available) is done through TCP over a specified port on each server.

Examining Supported Databases

Listed here are the services that do not support database mirroring, simply because the data associated with these services do not reside in a database. In other words, they are not needed for a restore: No information is stored or needed for these services because they are stateless and can simply start up and restart anytime without the need to store any data.

  • Visio Graphics Service

  • Access Services

  • Excel Services

  • Word Viewing Service

  • PowerPoint Service

  • State Service

Considering Performance and Scalability

With the increased number of configuration and service databases in SharePoint 2010, it is recommended that administrators thoroughly test the hardware capabilities of their SQL servers for performance and scalability issues when creating database mirroring sessions. Although Microsoft has stated that the practical maximum number of mirrored databases should not exceed 50, this number will vary depending on the following factors:

  • Network latency— It is recommended that network latency between the principal server and mirror server not exceed 1ms. This applies to synchronous mirroring only.

  • Network bandwidth— It is recommended that the network bandwidth between the principal server and mirror server be at 1Gb per second and less than 1ms of latency for synchronous mirroring. Asynchronous mirroring does not have these same requirements, but does require sufficient bandwidth to handle the flow of data from principal to mirror.

  • Memory— The amount of memory on both the principal server and mirror server should follow the hardware recommendations for deploying a SharePoint 2010 farm.

  • Processing power— Two threads are created for each database mirroring session; therefore, sufficient processing power is necessary on both the principal and mirror server to handle each database mirroring session without severely effecting performance.

  • Disk I/O— Because database mirroring involves writing potentially large amounts of logs to disk, it is recommended that disk I/O is optimized for faster disk access.

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