Safeguarding Confidential Data in SharePoint 2010 : Examining Supported Topologies

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A drastic improvement for SharePoint in terms of high availability is the full support of database mirroring. Content databases, configuration databases, and the majority of the service application databases can now be mirrored to provide for automatic data redundancy, provided that synchronous mirroring is used, because the config database and other noncontent databases need to be in exact alignment with each other.

If using asynchronous mirroring, however, only content databases can be supported for mirroring.

Using these concepts, there are effectively three types of mirroring topologies supported for SharePoint content, as discussed in the following sections.

Single Data Center High-Availability Model

In this model, shown in Figure 1, SQL mirroring is used solely to create a backup copy of the SharePoint databases so that they can be used to failover the environment in the event of a problem on the principal SQL server. Because synchronous DB mirroring is used, all SharePoint databases (excluding a few services databases that cannot be mirrored; more on this later) can be mirrored from the principal server to another.

Figure 1. Examining the single-site synchronous mirroring farm example.

This model requires two distinct SQL instances, and uses a SQL witness server to fail over from the principal to the mirror databases in the event of a failure. Because all SharePoint servers are in the same data center, there are only two SharePoint Web/Query/Service App servers in the farm.

Cross-Site High-Availability Model

In the next model, illustrated in Figure 2, the same concepts apply, except that the SQL mirror, witness, and additional SharePoint farm members are physically housed in a separate site. This is an ideal model, but it requires a backup data center that is physically close by because the network latency must be less than 1ms and the bandwidth between sites must be verifiably above 1Gb at all times.

Figure 2. Examining the cross-site high-availability SQL mirroring model.

In this model, if the primary data center were to completely fail, the SharePoint environment would continue to run on the synchronously mirrored databases in the backup data center.

As a side note, Microsoft has supported enviroments with latency levels up to 10ms, but it is critical that there not be spikes in the WAN traffic and that there is guaranteed bandwidth and low latency because these spikes can cause transactions to timeout on the production side of the SQL mirror. That said, the official Microsoft stance at the time of this writing is that 1ms of latency is required.

Multiple-Farm Cross-Site Model

In the next supported SQL mirroring model, shown in Figure 3, only the SharePoint content databases are mirrored to a remote location, using SQL Enterprise edition’s asynchronous mirroring. Failover to the remote site is manual, and involves attaching the content databases to a new farm that is identically configured to the main production farm.

Figure 3. Examining the multifarm cross-site SQL mirroring model.

This model is ideal for environments that are separated by greater distances or that don’t have the necessary bandwidth to support synchronous mirroring. A suboption to this model is one where the failover farm itself is only provisioned in the event of a site outage, rather than built as a “warm” farm.


These three models are supported using native Microsoft technologies. A broad third-party space exists that provides tools that allow for full two way replication of data between multiple SharePoint farms that can provide for similar or greater DR and HA functionality.

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