Moving the Active Database Copy to another DAG Member in Exchange Server 2010
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The ability of a database availability group DAG to contain as many as 16 Mailbox servers, combined with the ability to extend a DAG across multiple physical locations and Active Directory sites, provides a large number of architectural design possibilities for DAGs.
Four-member DAG that provides high availability within a single datacenter by locating all members in the same datacenter. Exmon exchange 2010 dag DAG that provides high availability within a single datacenter, and site resilience for that datacenter, by locating two of the members in the primary datacenter and two of the members in exmon exchange 2010 dag second datacenter. The design you use for your DAGs and the distribution of mailbox database copies will be based on your organization's service level agreements SLAs and the recovery time objective and recovery point objective for the mailbox service and data as stated in those SLAs.
Looking for management tasks related to high availability and site resilience? Two-member DAGs are best suited for organizations that require some form of high availability for mailbox services and data, but that don't require site resilience.
This configuration works especially well in small office and branch office deployments because it enables redundancy for the Client Access, Mailbox, and Hub Transport server roles using only two Exchange servers.
The following figure illustrates this configuration. Although it's supported to co-locate the Unified Messaging server role, we don't recommend that configuration for performance reasons. To achieve high availability for Client Access and Hub Transport server roles, some form of load balancing should be used between the clients and those server roles.
Because these server roles are co-located with a Mailbox server that's a member of a DAG, Windows Network Load Balancing can't exmon exchange 2010 dag used because Network Load Balancing and Windows failover clustering can't be installed on the same server. Instead, a exmon exchange 2010 dag Network Load Balancing solution must be used for example, a hardware load balancer or a third-party software-based load balancer.
As with all DAGs that contain an even number of members, a two-member DAG requires a witness server to maintain quorum. The witness server not pictured is a Windows server that isn't and will never be a member of the DAG. For exmon exchange 2010 dag, smaller organizations that use this configuration may use a file server or a directory server as the witness server. Quorum is maintained as long as more than half of the quorum voters are available and in communication. A two-member DAG with a witness server exmon exchange 2010 dag three exmon exchange 2010 dag voters.
Exmon exchange 2010 dag DAG member and the witness server can vote exmon exchange 2010 dag they are available exmon exchange 2010 dag in communication. Therefore, a two-member DAG can survive the failure or outage of a single voter for example, either of the DAG members, or just the witness server without an interruption in service. However, the loss of two of the voters for example, a DAG member and the witness server will result in a exmon exchange 2010 dag of quorum, which will result in an interruption in service.
A four-member DAG in a single datacenter deployment provides greater resilience to failures than a two-member or three-member DAG. Larger DAGs inherently provide greater resilience because they can sustain more failures without an interruption in service. Whereas a two-member or three-member DAG can exmon exchange 2010 dag the loss of only a single voter without losing quorum and compromising service, a four-member DAG, which by definition has five quorum voters, can sustain the loss of two voters without losing quorum and compromising service.
The following figure illustrates a four-member DAG with all members located in a single datacenter. Using a four-member DAG, you can create a maximum of four copies of each database. This is exmon exchange 2010 dag sufficient number of database copies to enable the use of alternate data protection scenarios, such as flexible mailbox protection. Flexible mailbox protection enables you to combine the Microsoft Exchange Server high availability and Extensible Storage Engine ESE resilience features with other built-in protection features, such as lagged mailbox database copies, retention policies, the Recoverable Items folder, and the hold policy, to create a solution that can reduce the need for other forms of protection, such as using Redundant Array of Independent Disks RAID or making data backups.
For more information about flexible mailbox protection, see Understanding Backup, Restore and Disaster Recovery. A four-member DAG extended across two datacenters provides both datacenters high availability and site resilience for the mailbox services and data. This configuration is illustrated in the following figure. The witness server for the DAG should be located in the primary datacenter. Generally, the primary datacenter is the datacenter containing the majority of the user population.
Using a witness server in exmon exchange 2010 dag primary datacenter enables continued functionality for the majority of the user population in the event of a wide area network WAN outage. You can use multiple DAGs to eliminate the WAN as a single point of failure and to allow service and data access to remain functional for multiple datacenters in the event of a WAN outage. For more information, see the next example. You can use router access control lists ACLs to block this traffic.
In this example, the Exchange server roles are deployed on dedicated hardware. As illustrated in the previous example, using a single four-member DAG extended across two datacenters can provide high availability and site resilience for the mailbox services and data. However, if a WAN outage occurs, only the primary datacenter retains service because it contains the majority of the voters. The datacenter with the minority of voters loses majority, and the DAG members in that datacenter lose quorum and go offline.
To deploy highly available Mailbox servers in a multiple datacenter environment, where each datacenter is actively serving a local user population, we recommend that you deploy multiple DAGs, where each DAG has a majority exmon exchange 2010 dag voters in a different datacenter, as illustrated in the following figure.
Although multiple DAGs can use the same witness server, multiple witness servers in separate datacenters are used to maintain service to each datacenter's local user population in the event of a WAN outage. If all network connectivity is lost between Redmond and Portland, the following occurs:.
As previously mentioned, larger DAGs inherently provide greater resilience because they can sustain more failures without an interruption in service. One design strategy that can help increase resilience when dealing with DAG member failures is to leverage the existing Hub Transport servers in the DAG's primary datacenter.
This strategy involves adding the Mailbox server role without any databases or database copies exmon exchange 2010 dag the Hub Transport server, and then adding that server to the DAG. In this scenario, the Mailbox server role is being used only for voting and quorum purposes. For example, consider a four-member DAG extended across two datacenters. The primary datacenter contains two DAG members and the witness server, and a second datacenter contains two DAG members.
As illustrated in the following figure, there are five quorum voters. Therefore, this DAG can lose two voters and still exmon exchange 2010 dag quorum. If the DAG loses a third voter, it loses quorum and requires manual administrative intervention to restore service. At this point, you don't create any production mailbox databases on these servers.
You also don't replicate any database copies to these servers. In this configuration, you can delete the default mailbox database and stop the Microsoft Exchange Information Store service which can also be optionally disabled. After the Mailbox servers that don't contain databases are added as members of the DAG, they become participants in quorum for the DAG. In this configuration, DAG1 now has seven quorum voters.
As a result, it can lose three servers and still maintain quorum. This site uses cookies for analytics, personalized content and ads. By continuing to browse this site, you agree to this use. Office Office Exchange Server.
Not an IT pro? United States English Sign in. The content you requested has been removed. Database Availability Group Design Examples. Understanding Datacenter Activation Coordination Mode. Database Copy Layout Design. Collapse the table of content. This documentation is archived and is not being maintained. You can use design examples for DAGs in a variety of exmon exchange 2010 dag Two-member DAG, which is suited for small office and branch office exmon exchange 2010 dag Four-member DAG that provides high availability within a single datacenter by locating all members in the same datacenter Four-member DAG that provides high availability within a single datacenter, and site resilience for that datacenter, by locating two of the members in the primary datacenter and two of the members in a second datacenter The design you use for your DAGs and the distribution of mailbox database copies will be based on your organization's service level agreements SLAs and the recovery time objective and recovery point objective for the mailbox service and data as stated in those SLAs.
Two-member database availability group There are several aspects worth noting about this configuration: Four-member database availability group Using a four-member DAG, you can create a maximum of four copies of each database. Four-member database availability group extended across two sites There are several aspects worth noting about this configuration: If all network connectivity is lost between Redmond and Portland, the following occurs: Seven-member DAG using three Mailbox servers that don't contain databases At this point, you don't create any production mailbox databases on these servers.
Although the Microsoft Exchange Information Store service isn't needed for a Mailbox server that doesn't contain a database to participate in quorum voting, the Microsoft Exchange Replication service must be running for the Mailbox server to participate in quorum and DAG functions. Is this page helpful?
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