Creating databases copies should be done according to a high-availability plan. A high-availability plan should be created that identifies the level of redundancy required for your environment. If JBOD Just a Bunch of Disks will be used to store database files, additional copies of the database should exist on other servers to sustain a disk failure. One of the options available when configuring mailbox database copies is to configure a lag time of up to 14 days.
This lag time is the time that the transaction logs will be held before being committed to the database copy. By delaying committing the logs to a database copy, you have the capability to recover the copy to a point in time using the copy rather than having to pull data from tape-based backup media. Lagged database copies are deployed to protect from logical corruption. Database logical corruption and store logical corruption are the two types of logical corruption that can occur in the Exchange database.
If you use multiple database copies and Single Item Recovery, only the extremely rare catastrophic store logical corruption case remains unaddressed. In the following scenarios lagged database copies can be used to recover data:. You should deploy lagged copies to mitigate a specific risk and lagged copies are usually not needed if you are also deploying a third-party backup solution.
Lagged copies should not be treated as another high-availability database copy and should not be activated for the following reasons:. Lagged copies have storage implications as enough space must be available to store the transaction logs for lag period.
However, rather than just meeting those requirements, it is best practice to have at least enough room for three additional days of transaction logs, to provide for potential truncation failures or periods of excessive log file generation. Block Mode Introduced in Exchange Service Pack 1 SP1 , continuous replication—block mode reduces the exposure of data loss on failover by replicating all logs writes to the passive database copies in parallel to writing them locally.
In other words, block mode replicates the transactions to the database copies as they are being written to the active local transaction log files. Enabling and disabling block mode is done automatically by the log copy process by database. Block mode will automatically become active when continuous replication file mode is up-to-date with the database copies.
The replication transport is the same when granular replication is enabled or disabled. The benefit of block mode is that it can dramatically reduce the latency between the active copy and the passive copy while also reducing the possibility of data loss during a failover and the time it takes to perform a switchover. Exchange supports the use of a single network adapter and path for DAG members. However, to provide network redundancy as well as the ability to separate replication and MAPI communication, multiple network adapters and networks subnets are recommended.
After the network hardware is in place and configured and windows failover clustering has detected the changes, these additional physical networks can be configured by setting up additional DAG networks within Exchange.
Regardless of location, each DAG member cannot have round-trip return network latency greater than milliseconds ms. This keeps replication communication from interfering with storage operations.
A DAG network can be configured in a couple different ways. The previous list suggested having at least two networks defined: one network dedicated for MAPI communication and one network dedicated for replication, as shown in Figure If all of the replication networks go offline or fail the MAPI network will be used for replication. When a highly available mailbox database failure occurs the PAM will attempt to perform a failover of the database.
Before attempting to select a suitable copy to activate the attempt copy last logs ACLL process occurs. This call requests to see whether the servers are available and healthy and determines the LogInspectorGeneration value for the database copy.
The last active mailbox database copy is used to copy any missing log files to the copy selected by Active Manager for activation. The AutoDatabaseMountDial value has the following three potential values:. BestAvailability This value allows the database to be automatically mounted if the copy queue length is less than or equal to The copy queue length is the number of logs that the passive copies recognize and have not been replicated.
When the copy queue length is less than or equal to 12, Exchange Server attempts to replicate the remaining logs to the passive copies and mount the database. This is the default value. GoodAvailability This value allows the database be automatically mounted immediately after a failover if the copy queue length is less than or equal to six. When the copy queue length is less than or equal to six, Exchange Server attempts to replicate the remaining logs to the passive copy and mount the database.
Lossless This value does not allow a database to mount automatically until all logs generated on the active copy have been copied to the passive copy. If the number of lost logs falls outside the configured AutoDatabaseMountDial value, Exchange Server does not mount the database until either missing log files are recovered or an administrator manually mounts the database and accepts that the loss of data is larger than the AutoDatabaseMountDial setting. It may seem counterintuitive to list the Best Availability as allowing for 12 missing transaction logs, and Good Availability as only allowing 6.
In this case, availability is referring to the database being mounted and available, not to the possibility of lost data. In most enterprise environments, data loss is less acceptable than the loss of service. You must decide whether to keep the database available by allowing it to mount despite potential data loss or to leave it unavailable and wait for manual recovery of missing log files.
When an active database failure occurs, Active Manager uses a set of selection criteria to determine which copy should be activated. It would make sense that Active Manager attempts to locate the best database copy to perform the quickest failover that is least likely to lose data.
Active Manager uses a complex sorting system to determine which copy to make active. When a failover occurs, Active Manager uses several sets of selection criteria to determine which database copy to activate. During the process for selecting the best copy to activate, Active Manager will:. The first option, switch parameter -BalanceDbsByActivationPreference , just activates the copy that has the lowest ActivationPreference value without taking into account Active Directory site balance.
The script will attempt to minimize an active copy imbalance during the redistribution process; this will help prevent a single node from being overwhelmed with active copies during this process. In large environments you may want to limit which servers can host an active database in the event of a failure so that a database is not brought online in a secondary datacenter if you are performing maintenance on a server or the database is a lagged copy.
A database activation policy can be set on the Mailbox server, or only the database copy can be configured to not activate. IntrasiteOnly This prevents database failovers from copies that are not in the same Active Directory site. Unrestricted This allows any server in the DAG to be for database activation. This is the default configuration. These policies only affect how Active Manager calculates where to activate database copies.
An administrator can manually mount the database on a server that has the activation policy set to Blocked. The server auto activation policy is usually used during periods of maintenance when you do not want a database copy to be automatically activated on a specific server.
The second way to control database activation is to suspend database activation on a specific copy of the database. Suspending activation for a specific database copy should be done on copies that you do not want to be activated automatically, such as lagged database copies. Unlike setting an activation policy on the Mailbox server, suspending activation on a database copy cannot be mounted directly by an administrator, as shown in Figure However, this block can be reset in two ways: when the database copy is reseeded or if replication is suspended and then resumed.
In case failure occurs and some transaction logs are not replicated to the passive copy, the transport dumpster is used to redeliver any recently delivered e-mail.
If a database failure occurs, a request is made to the Hub Transport servers to redeliver any lost e-mail messages. The transport dumpster only retains e-mail that has already been delivered. As soon as I shut down MS1 all works fine and the e mails that have been sent before when MS1 was up arrive to the recipient after three hours. Note that Exchange in MS1 is in on-premises mode.
Excuse for my English. Great details! I have another scenario. What is the best option for the replication NICs on the vms to interface with the physical server for seeding and replication. The vm network currently is one subnet. Does the seeding and DB copy happen as soon as you add the second server? I then want to use the DAG to minimize downtime to upgrade the systems to the latest SP to prepare for a Hybrid mode and a transition to O I have a small network with DC1 OS.
Win SBS standard and Exchange I have two virtual servers , each is Exch Sp1 multi-role running on windows sp1. Each how i configuration clustring. I created a DAG on exchange on winr2 but dag networks are not created. I have two virtual servers , each is Exch Sp3 multi-role running on windows R2 sp1. Each has only one network card assigned. However, the two servers are on different AD sites and on different subnets. Dear Paul, Thank you very much for the easy-to-follow guide.
Your expert comments will be highly appreciated. I would like to ask : 1. Is it enough to assign IP What would happen to EDGE subscription? How about certificate requirement for the new DAG member? I would like to know he steps to be followed, especially in terms of Quorum Configuration when we add a new node mailbox server to a 2 node DAG in Exchange Hi Paul, Thank you for all these clear explanations.
Great post. The DAG is working fine. The server1 is uninstalled in Control Panel — so no Exchange Roles. All production environment are up and running on EX so no crisis — but wondering about the -configurationonly switch when removing DAG-member.
What I would do: 1. Migrate mailboxes from old mailbox server to databases in the DAG 3. Decommission old mailbox server 4. Migrate CAS and Transport from old server to new load balanced servers 5. I added two new servers on the DAG. I have two Exchange server. One is Exchange and other is Exchange Can I configure DAG in that environment.
Great article! Thanks in advance. Hey Paul. Thanks for the quick response! Yes… manual failover seems to work and right now all active databases are on a single mail server. Again… great article and thanks for the assistance.
Thanks for this article. Currently I have one exchange server running all of the roles. I would like to add a second server and create a DAG. Question number one is can I have the CAS and HT roles stay on my current machine and have the new server be just a mailbox server and part of the DAG with the existing mailbox server role on the existing server? I know people have asked about having two servers with all the roles and then needing a hardware loadbalancer for the CAS array, but in my scenario I would just have one CAS and a two server DAG.
If that could work, I am guessing I would still need a third server to act as the File Share Witness. Can this server be at a different site? We have one Active Directory forest and domain. We were planning to add another exchange server with all roles MB, CAS, HUB with high end configuration to this setup for choosing one of the option — 1 We want to move all to new server and decommission the first server.
Could you please advice and share the implementation steps for the first option, if that is not viable then how we can implement the second option in this setup. The external one. How many microsoft server licenses we required to operate this scenario? Currently we have a script, when ever cluster group moves to DR, it will failover to DC node and notify…our million dollar question is when I have two nodes and FSW in production site, if I stop cluster service why cluster group is getting failed over to DR node instead of second node in the DC?
Two production nodes are in DC site and other two are in DR site. We have a file share witness configured in DC site, quorum model is Node with file share majority. We have two exchange DB copies active healthy on two production nodes and DR copies are healthy but not active. We have a requirement to have cluster group online always in DC nodes. Why it it getting failover to DR site? If both sites has equal amount of votes how cluster will get formed and who will own the cluster group?
Pls help us to understand this…. Possible owners of cluster group are N1, N2, N3, N4. I understand next node will be selected based on cluster arbitration, But as per Many MS articles Next possible node will own the cluster group. Here Node 2 is next possible owner, but why Node4 in DR node Id4 is owning the group, why not next possible owner?..
In similar way again if I stop on Node4, it should go to next possible owner Node1 , why is it going to Node Modifying underlying cluster properties is probably unsupported. If you have a hard requirement for this perhaps you could simply write a script that regularly checks for cluster group ownership and moves it when necessary. Error: A source-side operation failed. Error Content indexing operation failed with the following message: The seeding operation encountered an error while trying to contact the search service.
I used this article to configure my DAG, everything was succesful but I have discovered an issue. Please use the Failover Cluster Manager snap-in to check the configured properties of the cluster network. The workaround I found to get this resource online is moving the replication subnet into the MAPI group in the DAG Networks, Bring the resource online and move the subnet back to the replication group.
Do you know why we are getting the replication IP resource as failed and how to resolve this issue? I have configured the DAG with 2 IP Address, the first one pointing to the corp network and the 2nd to the replication network. The 2nd one is used to perform the backup with Symantec Netbackup trough the replication network Is this OK? The environment also has voicemail system with unified messaging using a MAPI gateway as the interface which is pointed to the CAS for authentication.
The MAPI gateway has a superuser account that is used to handle all requests for mailbox users. The tried rebooting the MAPI gateway, etc and only after backing out did requests get processed. Is there something I can direct their attention to or troubleshooting tips? The service account used by the voicemail system likely needs some specific permissions in place on the mailbox databases.
As always appreciate your articles. Because a subnet matching The Some third-party applications connect to the cluster administrative access point to perform management tasks, such as backup or monitoring. If you do not use any third-party applications that require a cluster administrative access point, and your DAG is running Exchange or Exchange on Windows Server R2, then we recommend creating a DAG without an administrative access point.
DAGs are also configured to use a witness server and a witness directory. The witness server and witness directory are either automatically configured by the system, or they can be manually configured by the administrator.
By default, a DAG is designed to use the built-in continuous replication feature to replicate mailbox databases among servers in the DAG. After this mode is enabled, it can't be disabled.
DAGs make use of Windows failover clustering technology, such as the cluster heartbeat, cluster networks, and the cluster database for storing data that changes, such as database state changes from active to passive or vice versa, or from mounted to dismounted and vice versa.
As each subsequent server is added to the DAG, it's joined to the underlying cluster, the cluster's quorum model is automatically adjusted by Exchange, and the server is added to the DAG object in Active Directory. After Mailbox servers are added to a DAG, you can configure a variety of DAG properties, such as whether to use network encryption or network compression for database replication within the DAG. After you create mailbox database copies, you can monitor the health and status of the copies using a variety of built-in monitoring tools.
In addition, you can perform database and server switchovers. Underneath every DAG is a Windows failover cluster. Failover clusters use the concept of quorum, which uses a consensus of voters to ensure that only one subset of the cluster members which could mean all members or a majority of members is functioning at one time.
Quorum isn't a new concept for Exchange Server. Highly available Mailbox servers in previous versions of Exchange also use failover clustering and its concept of quorum. Quorum represents a shared view of members and resources, and the term quorum is also used to describe the physical data that represents the configuration within the cluster that's shared between all cluster members.
As a result, all DAGs require their underlying failover cluster to have quorum. In this event, administrator intervention is required to correct the quorum problem and restore DAG operations. Quorum is important to ensure consistency, to act as a tie-breaker to avoid partitioning, and to ensure cluster responsiveness:.
Answered by:. Archived Forums. Exchange Server This forum provides a place for you to discuss the Exchange You are welcome to come and post questions and comments about your experience with this software. Sign in to vote. Friday, April 30, AM.
It's running right now so I'm sure of that : But thanks for clarifying the DB copies question. Marked as answer by lukabike Friday, April 30, PM.
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