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Designing a Hugely Accessible Database Copy LayoutDesigning a Hugely Available Database Duplicate LayoutWelcome to BlogEngine.Internet 1.6.0
One from the goals of Trade 2010 mailbox resiliency is to reduce information loss. In Trade 2010 SP1 we added continuous replication block mode to aid additional lessen info reduction whenever a failover happens. Even so, on a very active mailbox database using a substantial log generation price, there's a larger chance for info damage if replication towards the passive database copies are not able to keep up with log generation.

One situation that will introduce a higher log generation charge is mailbox moves. Consider the subsequent two examples:
Example one: As an administrator you decide to move a mailbox from DatabaseA to DatabaseB. The mailbox transfer completes productively. Nevertheless, instantly adhering to the transfer operation, the server hosting the energetic copy of DatabaseB fails. One more duplicate of DatabaseB is activated with data loss because AttemptCopyLastLogs cannot comprehensive productively. As a result, a part from the mailbox info might be lost. Instance two: Being an administrator you determine to maneuver a selection of mailboxes in your Trade 2010 RTM surroundings, whose entire info arranged suit on a single 1MB log file. You timetable the moves and the mailboxes are efficiently transferred from DatabaseA to DatabaseB. Instantly next the transfer, DatabaseB’s server fails. Another copy of DatabaseB is activated with info reduction because AttemptCopyLastLogs can't full productively. At the time in the failure, the lively log file that contained all in the knowledge associated with the mailbox moves and the associated transactions was not replicated towards the other copies. Consequently, the copy mounts, but the transferred mailboxes are not inside DatabaseB. In addition,Tiffany Earings, since the Exchange Mailbox Replication service marked the mailbox moves as comprehensive, the mailboxes are no longer within DatabaseA.
As you can imagine, these are serious data damage issues. Thankfully, we thought of these while developing Trade 2010.
Knowledge Guarantee API & the Mailbox Replication Service
Exchange 2010 includes a Knowledge Guarantee API that is used by services like the Mailbox Replication service (MRS) to check the health with the database duplicate architecture based on the defined setting from the database, as set by the system or an administrator. Specifically, the Information Guarantee API can be used to:
Check Replication Health - Confirm that the prerequisite number of database copies is obtainable. Check Replication Flush - Confirm that the required log files have been replayed against the prerequisite number of database copies.
When executed, the API returns the next information back towards the calling application:
Status information returns one from the adhering to values: Retry: returned therefore of transient errors that prevent a condition from being checked against the database. Satisfied: returned when the database meets the required conditions, or if the database is not replicated. NotSatisfied: returned when the database does not meet the required conditions. In addition, information is provided back towards the calling application as to why the NotSatisfied response was returned. How long the calling application should wait before attempting to check again. If duplicate information has not been collected, the default wait time is 10 seconds. If no healthy database copies are found, the default wait time is two minutes. If a healthy copy is found, but is slightly behind in replication, the default wait time is one minute. The maximum possible wait time is 10 minutes. DataMoveReplicationConstraint
The value for the DataMoveReplicationConstraint property from the mailbox database determines how many database copies should be evaluated as part from the request. The DataMoveReplicationConstraint property has the following possible values:
None: This is the default value whenever a mailbox database is created. When set to None, the information guarantee API conditions are ignored. This setting should only be used for mailbox databases are not replicated. SecondCopy: At least 1 passive database duplicate must meet the data guarantee API conditions. This is the default value when you add the second duplicate of a mailbox database. SecondDatacenter: At least 1 passive database copy in yet another Active Directory site must meet the information guarantee API conditions. AllDatacenters: At least one passive database copy in each Active Directory site must meet the knowledge guarantee API conditions. AllCopies: All copies from the mailbox database must meet the data guarantee API conditions. Check Replication Health
When the Data Guarantee API is executed to evaluate the health in the database copy infrastructure, the following items are evaluated:
If the DataMoveReplicationConstraint is arranged to SecondCopy, then for a given replicated database at least one passive database copy must: Be healthy. Have a replay queue inside 10 minutes of replay lag time. Have a duplicate queue length less than 10 logs. Have an average duplicate queue length less than 10 logs. The average copy queue length is computed based on the number of times the application has queried the database status. If the DataMoveReplicationConstraint is set to SecondDatacenter, then for a given database at least one passive database copy in an additional Energetic Directory site must: Be healthy. Have a replay queue inside of 10 minutes of replay lag time. Have a duplicate queue length less than 10 logs. Have an average duplicate queue length less than 10 logs. If the DataMoveReplicationConstraint is arranged to AllDatacenters, then for a given database,Tiffany Brisbane, the active copy must be mounted, and a passive copy in each AD site must: Be healthy. Have a replay queue in 10 minutes of replay lag time. Have a copy queue length less than 10 logs. Have an average copy queue length less than 10 logs. If the DataMoveReplicationConstraint is set to AllCopies, then for a given database, the lively duplicate must be mounted, and all passive database copies must: Be healthy. Have a replay queue within 10 minutes of replay lag time. Have a duplicate queue length less than 10 logs. Have an average copy queue length less than 10 logs. Check Replication Flush
In Exchange 2010 SP1, the Information Guarantee API can also be used to validate that a prerequisite number of database copies have replayed the required transaction logs. This is verified by comparing the last log replayed timestamp with that in the calling service’s commit time stamp (in most cases,Tiffany Silver, this is the time stamp from the last log file that contains required info) plus an additional 5 seconds (to deal with system time clock skews or drift). If the replay time stamp is higher than the commit time, then the DataMoveReplicationConstraint is satisfied.

If replay time stamp is not greater than the commit time, then the DataMoveReplicationConstraint is not satisfied.
Mailbox Replication Service
MRS calls into the Knowledge Guarantee API several times throughout the lifetime in the transfer request. As documented in Understanding Move Requests,Kineda CSSMania, mailbox moves are performed as follows:
The Move Request updates Energetic Directory and injects a message in the system mailbox of a mailbox database in the target Lively Directory site. MRS will query the Knowledge Guarantee API to determine the health of the target database duplicate infrastructure. As long as the returned status is Satisfied, the transfer request will continue. MRS will begin the data transfer by cloning the mailbox structure in the target mailbox database. MRS will query the Info Guarantee API to determine the health from the target database duplicate infrastructure. As long as the returned status is Satisfied, the move request will continue. MRS will perform the initial synchronization by taking a snapshot with the source mailbox and replicating folders and content. Throughout this process, MRS will query the Knowledge Guarantee API every 10 seconds to determine the health from the target database duplicate infrastructure. As long as the returned status is Satisfied, the move request will continue. MRS will perform incremental synchronization events and replicate the delta changes (when compared with the initial snapshot). Throughout this process, MRS will query the Knowledge Guarantee API every 10 seconds to determine the health in the target database duplicate infrastructure. As long as the returned status is Satisfied, the transfer request will continue. MRS will lock the source mailbox. MRS will perform an incremental synchronization to obtain the changes made since the last synchronization event, in addition, to copying other knowledge structures within the mailbox. Beginning with SP1, MRS will force the target database to roll the energetic transaction log file if the log isn’t rolled naturally, thereby ensuring ongoing replication can replicate the log file data that contains the transferred mailbox synchronization info. MRS determines whether this activity has been successful by using the Check Replication Flush capability in the Data Guarantee API. MRS will query the Data Guarantee API to determine the health of the target database copy infrastructure. As long as the returned status is Satisfied, the move request will continue. MRS will update mailbox-enabled user account in Active Directory indicating the move is comprehensive. MRS will unlock the target mailbox. MRS will change the state in the mailbox in the source database to soft-deleted. This feature was additional in Exchange 2010 SP1 and ensures that in the event the target database is misplaced,Tiffany, you can still recover the mailbox from its previous database.
For Steps 1 through 4, if at any time the Info Guarantee API returns a NotSatisfied or a Retry response, MRS will queue the transfer request and retry the query every 30 seconds. MRS will queue the move request for up to 15 minutes before failing the transfer request. If a Satisifed response is returned within the 15 minute stalling period,Tiffany Co Rings, MRS will automatically resume the move request.

During Step six, MRS will wait a maximum of 30 minutes for that Info Guarantee API to return a Satisfied response (retrying the query every 10 seconds). If a Satisfied response is not returned, MRS will fail the mailbox transfer.

When a transfer request has failed it will not be resumed automatically by MRS. Prior to initiating a Resume-MoveRequest, the administrator should execute the Get-MoveRequestStatistics to troubleshoot why the transfer request failed. After addressing the cause of the failure, the administrator can then execute the Resume-MoveRequest.

Note that if both the primary mailbox and the personal archive are being moved at the same time, both completions need to be guaranteed for your total transfer request to proceed.
Determining the Appropriate DataMoveReplicationConstraint for your Setting
You should configure the DataMoveReplicationConstraint property on each mailbox database according to the following:
If you are deploying...Set DataMoveReplicationConstraint to Mailbox databases that do not have any database copies None A DAG in just one Lively Directory site SecondCopy A DAG in multiple datacenters using a stretched Energetic Directory site SecondCopy A DAG that spans two Energetic Directory sites and you will have hugely offered database copies in each site SecondDatacenter A DAG that spans two Lively Directory sites and you will have only lagged database copies in the second site SecondCopy
This is because the Info Guarantee API will not guarantee info being committed until the log file is replayed into the database copy and due for the nature with the database duplicate being lagged this constraint will fail the transfer request, unless the lagged database copy ReplayLagTime value is less than 30 minutes. A DAG that spans three or more Active Directory sites and each site will contain extremely available database copies AllDatacenters