The specific symptoms are as follows:
- Symptom 1:
DCDIAG reports that the Active Directory Replications test has failed with error status (8461): The replication operation was preempted.
Sample error text from DCDIAG resembles the following:
Testing server: <site>\<DC name>
Starting test: Replications
* Replications Check
REPLICATION LATENCY WARNING
[Replications Check,<DC name>] This replication path was preempted by higher priority work.
From <source DC> to <destination DC>
Naming Context: DC=<DN path>
The replication generated an error (8461):
The replication operation was preempted.
Replication of new changes along this path will be delayed.
Progress is occurring normally on this path.
- Symptom 2:
REPADMIN.EXE reports that the last replication attempt was delayed for a normal reason, result 8461 (0x210d).
REPADMIN commands that commonly cite the 8461 status include but are not limited to:
- REPADMIN /REPLSUM
- REPADMIN /SHOWREPL
- REPADMIN /SHOWREPS
- REPADMIN /SYNCALL
- Symptom 3:
Repadmin /rehost fails and generates status code 8461.
- Symptom 4:
Repadmin /queue output reveals one or more task that have a status of "PREEMPTED."
 Enqueued 2011-11-26 06:05:55 at priority 40 SYNC FROM SOURCE NC dc=west,dc=contoso,dc=com DSA Boulder\BoulderDC DC DSA object GUID c7f89ed3-0f4a-4ae7-8a20-b025b4556358 DSA transport addr c7f89ed3-0f4a-4ae7-8a20-b025b4556358._msdcs.contoso.com ASYNCHRONOUS_OPERATION NEVER_COMPLETED NEVER_NOTIFY PREEMPTED
- Symptom 5:
The "replicate now" command in Active Directory Sites and Services (DSSITE.MSC) fails and generates the following error message:The replication operation was preempted.
Dialog title: Replicate Now
Message text: The following error occurred during the attempt to synchronize naming context <DNS name of directory partition> from domain controller <source DC>
to domain controller <destination DC>:
The replication operation was preempted.
- Symptom 6:
Events in the Directory Services event log cite the error status 8461.
Event Source and Event ID Message NTDS Replication 1839
The following number of operations is waiting in the replication queue. The oldest operation has been waiting since the following time. Time: <date> <time> Number of waiting operations: <value> This condition can occur if the overall replication workload on this domain controller is too large or the replication interval is too small.
NTDS Replication 2094
Performance warning: replication was delayed while applying changes to the following object. If this message occurs frequently, it indicates that the replication is occurring slowly and that the server may have difficulty keeping up with changes.
Source: NTDS ReplicationEvent ID 1839Type: WarningDescription:The following number of operations is waiting in the replication queue. The oldest operation hasbeen waiting since the following time.Time:
While this issue is common and usually transient, some other AD replication problems can cause a backlog in the queue. If this occurs, you might start seeing replication tasks being preempted frequently. Frequent logging of event 2094 "Performance warning" (sample event are shown in the "Symptoms" and "Resolution" sections) is another indication that troubleshooting may be needed.
Investigate those problems
Explanation of repadmin /queue and replication priority
Analyze queue output over time to determine whether tasks are being processed
Explanation of repadmin /showrepl /verbose
|Active Directory replication has been preempted.||The progress of inbound replication was interrupted by a higher priority replication request, such as a request generated manually with the repadmin /sync command.||Wait for replication to complete. This informational message indicates normal operation.|
- Too many partners
- Too frequent of object and attribute updates
- Frequent updates combined with inter-site change notification which results in a high rate of redundant change notifications
- Small replication schedule window
- Disk and or memory performance
- Network performance
If the status 8461 never clears, there is a lot of work to do to determine the correct path to take. This issue requires advanced knowledge of multiple troubleshooting tools. It may be necessary to seek the help of Microsoft Support to assist with the data analysis process.
You will have to determine the cause before you implement any steps to resolve an underlying problem. The cause of the replication status 8461 can occur in any of the following scenarios:
- Transient condition
- Replication load
- Consistent Load
- Temporary Load
- Performance issue
- OS Performance
- Disk Performance
- Network Performance
If replication tasks are queued. Look at the currently running task, and investigate.
Use event log data, repadmin output, and performance monitor to help isolate the cause of the problem. Determine how quickly updates are being processed and what rate of change.
ConsistentThe domain controller has too many replication partners or under too great a replication load. Symptoms of an overloaded DC would be:
- A replication queue that never clears even though replication tasks are processed in a timely fashion
Note You can use repadmin /queue over time and correlate this with performance data to identify this scenario.
- Frequent occurrence of replication status 8461
- Resolution: Reduce inbound connections (balance connections amongst hub-site DCs (ADLB.exe is useful here), add new DCs and re-balance the connections, deploy RODC in spoke sites, and decrease excessive replication of changes.
Excessive replicationAttributes that are very frequently updated. Identify attribute updates using verbose replication event log events (or using repadmin /showchanges) and then correlate with repadmin /showobjmeta for several objects on the destination DC. Look at the attribute identified in the event and look for a high version number, or get multiple logs for the same object throughout the day and see if the version number increases frequently.
913676 Event ID 2008 is logged in the Application log on a domain controller after you install Exchange 2003 Service Pack 2.
- Bulk changes infrequently
- After hosting a partition for the first time or during a rehost
Common symptoms for performance induced queue buildup include
Event ID 2094
Event Type: Warning Event Source: NTDS Replication Event Category: Replication Event ID: 2094 Description: Performance warning: replication was delayed while applying changes to the following object. If this message occurs frequently, it indicates that the replication is occurring slowly and that the server may have difficulty keeping up with changes. Object DN: CN=JUSTINTU,OU=Workstations,DC=contoso,DC=com Object GUID: 2530ee74-85e3-4276-15f2-ba6a310471eb Partition DN: DC=contoso,DC=com Server: 4e901384-2aa1-3008-c5a2-e37f9f67d7e0._msdcs.contoso.com Elapsed Time (secs): 13 User Action: A common reason for seeing this delay is that this object is especially large, either in the sizeof its values, or in the number of values. You should first consider whether the application can be changed to reduce the amount of data stored on the object, or the number of values.If this is a large group or distribution list, you might consider raising the forest version to Windows Server 2003, since this will enable replication to work more efficiently. You should evaluate whether the server platform provides sufficient performance in terms of memory and processing power. Finally, you may want to consider tuning the Active Directory database by moving the database and logs to separate disk partitions. If you wish to change the warning limit, the registry key is included below. A value of zero will disable the check. Additional Data Warning Limit (secs): 10 Limit Registry Key: System\CurrentControlSet\Services\NTDS\Parameters\Replicator maximum wait for update object (secs)Determine whether changes that are applied to the database are occurring slowly by using performance monitoring and repadmin /queue output. Correlate AD Replication counters with base OS performance counters (Disk, Memory, Network and CPU).
Queue contains 55 items. Current task began executing at 2011-11-26 01:55:33. Task has been executing for 508 minutes, 53 seconds.  Enqueued 2011-11-26 01:55:33 at priority 590 SYNC FROM SOURCE NC DC=corp,DC=contoso,DC=com DC Houston\5thWardDC DC object GUID c130e148-1e40-4a0e-be6d-356eec2be0bd DC transport addr c130e148-1e40-4a0e-be6d-356eec2be0bd._msdcs.contoso.com FORCE Enqueued 2011-11-26 06:05:55 at priority 40 SYNC FROM SOURCE NC dc=west,dc=contoso,dc=com DC Boulder\BoulderDC DC object GUID c7f89ed3-0f4a-4ae7-8a20-b025b4556358 DC transport addr c7f89ed3-0f4a-4ae7-8a20-b025b4556358._msdcs.contoso.com ASYNCHRONOUS_OPERATION NEVER_COMPLETED NEVER_NOTIFY PREEMPTED
Slow AD Replication troubleshootingThis issue requires advanced knowledge of multiple troubleshooting tools. It may be necessary to seek the help of Microsoft Support to assist with the data analysis process.
Terminology: Slow vs. latentIn slow AD replication, changes are committed to the Active Directory database slowly or replication tasks take a long time to process.
Common causes include:
- DC / OS performance problems
- Resource depletion
- Disk bottleneck
- AD database problems
- Logical or physical corruption
- Object or attribute issues
- DC load issues
- Handling too many clients
- Replication storm
- High rate of change to objects and attributes
- Full partition syncs
In latent AD replication, the DC is not notified about changes for a long time:
Common causes include:
- AD Topology Configuration (schedule, site links, replication schedule, disconnected topology)
This document and data collection strategy is meant to be used for troubleshooting Slow AD Replication.
Symptoms of slow AD Replication
Data collectionRepadmin Data
Use Repadmin /queue to document the queued replication tasks. Monitor the queue to see if there is a delay in processing replication tasks. Log all repadmin /queue output to the same text file so you have good historical data.
Repadmin /queue DCName >DCNameReplQueue.txt Choice /d y /t 300 Repadmin /queue DCName >>DCNameReplQueue.txt Choice /d y /t 300 Repadmin /queue DCName >>DCNameReplQueue.txt Choice /d y /t 900 Repadmin /queue DCName >>DCNameReplQueue.txt Choice /d y /t 900 Repadmin /queue DCName >>DCNameReplQueue.txt Choice /d y /t 1800Repadmin /queue DCName >>DCNameReplQueue.txt
Review the output to see whether replication tasks are processed in a timely manner. The top of the file contains the currently running task and the length of time it has been running. If the same task is always at the top of the output, you can use verbose output of
repadmin /showrepl to monitor the progress.
Repadmin /showrepl and the
/verbose option to monitor the last replication status and the number of changes that remain to be replicated.
Repadmin /showrepl /verbose DCNameDomainDN
Repadmin /showrepl /verbose 5thwardCorpDC dc=corp,dc=contoso,dc=com
To limit the output so that only the desired Source DC is displayed, use the following:
Repadmin /showrepl /verbose DCNameDomainDN SourceDcDSAObjectGUID
Repadmin /showrepl /verbose 5thwardCorpDC c7f89ed3-0f4a-4ae7-8a20-b025b4556358 dc=corp,dc=contoso,dc=com
Repadmin /showutdvecon the source and destination DC to determine replication delta.
Repadmin /showutdvec DCName DomainDN
repadmin /showutdvec LiverpoolDC1 dc=north,dc=fabrikam,dc=com
Obtain Repadmin /showutdvec /latency from the source and destination DC for the partition in question.
In the output, document the following:
- From source DCs showutdvec:
- USN # next to Source DCName
- From destination DCs showutdvec
- USN# next to SOURCE DCNanme
Dallas\2008DC1 @ USN 451265 @ Time 2013-07-10 13:30:43 Dallas\SourceDC @ USN 1126541 @ Time 2013-07-12 08:17:16 Houston\2012DC3 @ USN 469842 @ Time 2013-07-10 13:14:27 66a1b264-80b8-44f8-8356-9ebcd7a34f15 @ USN 32811 @ Time 2013-06-06 08:26:56 Dallas\2012DC2 @ USN 460219 @ Time 2013-07-10 13:30:44 Dallas\DestinationDC @ USN 1353465 @ Time 2013-07-11 14:16:40 Dallas\2003DC1 @ USN 15556 @ Time 2013-07-10 13:21:50
Dallas\2008DC1 @ USN 451265 @ Time 2013-07-10 13:30:43 Dallas\SourceDC @ USN 801224 @ Time 2013-07-11 14:17:04 Houston\2012DC3 @ USN 469842 @ Time 2013-07-10 13:14:27 66a1b264-80b8-44f8-8356-9ebcd7a34f15 @ USN 32811 @ Time 2013-06-06 08:26:56 Dallas\2012DC2 @ USN 460219 @ Time 2013-07-10 13:30:44 Dallas\DestinationDC @ USN 1359087 @ Time 2013-07-12 07:59:37 Dallas\2003DC1 @ USN 15556 @ Time 2013-07-10 13:21:50
SourceDC @ USN 1126541
SourceDC @ USN 801224
1126541-801224 = 325317
The destination DC is 325,317 USNs behind.
Note You can also get the Source DCs highestcommitedUSN from the Source DC by using this command:
repadmin /showattr SourceDC . /atts:highestcommittedusn DN: 1> highestCommittedUSN: 1126541
Create a new User Defined Data Collector set In Performance Monitor that uses the AD Diagnostics template.
The steps here detail how to set up a good set of baseline DC performance counters. You will need to modify some of the settings, such as duration and sample interval to fit your specific scenario.
How to Create a User Defined Data Collection Set
- Open Server Manager on a Full version of Windows Server 2008 or a later version.
- Expand Diagnostics > Performance > Data Collector Sets.
- Right-click User Defined and select New > Data Collector Set.
- Type in a name such as AD DS Diagnostics, and leave the default selection of Create from a template (Recommended) selected. Then, select Next.
- Select Active Directory Diagnostics from the list of templates and then select Next and follow the Wizard prompts (making any changes you think are necessary).
- Right-click the new User Defined data collector set and view the Properties.
- To change the run time, modify the Overall Duration settings in the Stop Condition tab, and then click OK to apply the changes.
Options to consider:
- Overall Duration –you can have the data collector stop after collecting for a set amount of time
- Limits –you can have the data collect stop after a time or size threshold is reached (with the option to have it automatically restart)
Setting limits is advantageous when you want to limit the log size.
- Restart the data collector set at limits
- Maximum Size
- Select your new User Defined data collector set.
- Right-click Performance Counter, and then select Properties.
Here you have the options of changing the Sample interval and adding or removing additional counters.
For this scenario, the default-sampling interval of 3 seconds should be sufficient. However, for much longer sampling times, 3 seconds is too frequent an interval.
All recommended counters are included in the default AD Diagnostic’s collector set with three exceptions:
- Database ==>Instances(lsass/NTDSA)\ *
For LogicalDisk: all instances is not required - System drive and drives where database and logs are stored should be included at minimumSecurity System-Wide Statistics\*
- Security System-Wide Statistics\*
- In Performance Counter Properties, select Add.
- Expand Database ==>Instances (all counters should be highlighted).
- Under Instances of selected object, select lsass/NTDSA
- Select Add, and then click OK.
- Add the LogicalDisk and Security System-Wide Statistics objects also.
When you are ready to begin collecting performance data, start your newly defined Collection Set:
To start your newly defined Data Collection Set from the MMC:
- In the Performance Monitor mmc, navigate to Performance / Data Collector Sets / User Defined
- Right click the new collection set AD DS Diagnostics and select Start.
- You can verify that it has started by selecting User Defined
AD DS Diagnostics should have a status of Running
After testing is complete, stop the AD DS Diagnostics Collection Set:
- In the Performance Monitor mmc, navigate to Performance / Data Collector Sets / User Defined.
- Right-click the new collection set AD DS Diagnostics, and select Stop. You can verify that it has stopped by selecting User Defined.
AD DS Diagnostics should go from a status of Running to Compiling and finally Stopped
The compiled report is viewable under Performance / Reports / User Defined / AD DS Diagnostics
The default path in Windows Explorer is here: %systemdrive%\PerfLogs\Admin\AD DS Diagnostics
Command Line instructions: Gather AD Diagnostics from the command line:
To START a collection of data from the command line issue this command from an elevated command prompt:logman start "user defined\AD DS Diagnostics" –ets To STOP the collection of data before the default 5 minutes, issue this command: (get at least one full five minute sample for this issue) logman stop "user defined\AD DS Diagnostics" –ets
Diagnostic data is logged here: C:\PerfLogs\Admin\AD DS Diagnostics\DateStamp
Sample Data Collection Script
logman start "system\Active Directory Diagnostics" -ets time /t >slow.txt repadmin /showrepl /verbose LiverpoolDC1 dc=north,dc=fabrikam,dc=com >slowrepl.txt repadmin /queue LiverpoolDC1 >>slow.txt repadmin /showutdvec LiverpoolDC1 dc=north,dc=fabrikam,dc=com >>slow.txt :start ping 127.0.0.1 -n 60 >NUL time /t >>slow.txt time /t >>slowrepl.txt repadmin /showrepl /verbose LiverpoolDC1 dc=north,dc=fabrikam,dc=com >>slowrepl.txt repadmin /queue LiverpoolDC1 >>slow.txt repadmin /showutdvec LiverpoolDC1 dc=north,dc=fabrikam,dc=com >>slow.txt goto start
Event log data
The default logging enabled in the directory services event log is useful to monitor for events that indicate slow application of changes. (EVENT X) Verbose diagnostic logging can be enabled to see what changes are currently being applied. Enabling diagnostic logging at the level mentioned in this article will cause the log to fill up rather quickly, so only enable it while actively troubleshooting this condition. To give an idea of rate of events logged with this level of verbosity:
A Directory Services event log configured to 100 MB wrapped in less than two minutes (1 minute 27 seconds). The log contained 195,728 events. Of all events, 189,340 were event ID 1412 (attribute addition).
- Increase the size of the Directory Services event log
- Size the event log so that the enhanced logging doesn't cause the log to wrap in too short of a period
- Enable AD Replication Diagnostic logging to 0x5:
HKLM\System\CurrentControlSet\Services\NTDS\Diagnostics5 Replication Events = 5
Export the Directory Services event log shortly after you receive the status 8461, and reduce the diagnostic logging to a suitable level.
Review the event log for the following:
How quickly are attribute values are written to the database? ->Directory Services event log Event ID 1412 or even better, use performance counter:DirectoryServices/DRA Inbound Properties Applied/sec
At diagnostic level 5 for Replication Events, for user object creation, around 25 or so event 1412's (depending on what was written at time of user creation) are written (one per attribute value). When all attributes have been added, the object creation event is logged (Event ID 1365).
The description section of the event contains the following data:
Internal event: The following object changes were applied to the local Active Directory Domain Services database. Property: 900dd (sAMAccountName) Object: CN=xtestingusers14167,CN=Users,DC=north,DC=fabrikam,DC=com Object GUID: 984a8f06-aa4b-4f80-8b40-0f78b5066ae0 Remote version: 1 Remote timestamp: 2013-07-10 14:24:31 Remote Originating USN: 540828
The Property section contains both the attributeID and the lDAPDisplayName of the attribute.
One event is written per value at this debug log level. Filter on the events and determine how many entries occur in a given period. Review the event details in order to determine if we are writing values for multiple attributes in order to instantiate an object or if we are writing to the same attribute across multiple objects. While this level of analysis can seem cumbersome, it can be useful in determining root cause. As an example, if you see that we are only writing a few events per second then that could indicate that transactions are being written to the database slowly or perhaps we have too many partners that are sending redundant changes (event ID 1239).
Notice that it is perfectly normal to see event ID 1239 when replication diagnostics is set to 0x5. If you filter out event 1239 and you see nothing else and you have a fairly long event log history then that may indicate a problem. This issue was observed by a customer with a large Active Directory environment that had inter-site change notification enabled. If you determine that there is a large number of events per second, replication is probably not affected by a performance problem.
If an event is logged that indicates a change is taking a long time to process Event ID, record the objectGUID, and then get the following output:
Repadmin /showobjmeta * "<GUID=ObjectGUID>" >objectmeta.txt
Review the output for recently modified attributes. Pay particular attention to attributes with frequently modified version numbers. An attribute that has a very high version count could indicate that frequent changes are being made to the attribute. If you suspect this, you can either view the attribute value to get some context as to why the attribute was changed, or you can let some time pass, and then get addition repadmin /showobjmeta output in order to check whether the version of the same attribute on the same object has increased further.
Object and attribute data:
Use a utility to output the object and attribute values. Then, review the attribute data for the attributes that have recently modified data. The following examples present two methods to do this.
Object attribute values from repadmin:
Repadmin /showattr DCName "<GUID=ObjectGUID>" /allvalues /long >objectByGuid.txt
Object attribute values from LDP
Connect and bind to the server in LDP and copy all the output for the object to a text file
Network related data
Tasklist /svc >nets.txt Netstat –anob >>nets.txtData AnalysisKey AD Replication specific Performance Counters
- DRA Inbound Full Sync Objects Remaining
- DRA Inbound Objects Applied/Sec
- DRA Inbound Objects / Second (Inbound Replication)
- DRA Inbound Objects Filtered / Sec (Suggests all New Attributes)
- DRA Outbound Bytes Total Since Boot
|DirectoryServices\DRA Pending Replication Synchronizations||Indicates the number of directory synchronizations that are queued for this server. This counter helps identify replication backlogs—the higher the number, the larger the backlog.||This counter should be as low as possible. If it is not, the server hardware is probably slowing replication.|
Use this counter to determine the replication queue. Repadmin /queue DCName also reports this information.
Gauging Current Performance:
|DRA Inbound Objects Applied/sec||Shows the number of objects received from neighbors through inbound replication and applied.|
|DRA Inbound Properties Applied/sec||Shows the total number of object properties (attributes) applied from inbound replication partners. |
You can use the two counters to monitor how quickly changes are being applied to the database.
|DirectoryServices\DRA Inbound Object Updates Remaining in Packet||Indicates the number of object updates received in the most recent directory replication update packet that have not yet been applied to the local server.||This counter indicates that the monitored server is receiving changes, but it is taking a long time to apply them to the database. This counter should be as low as possible. If it is not, it usually indicates that server hardware is slowing replication.|
|DirectoryServices\DRA Inbound Bytes Total/sec||Indicates the total number of bytes received per second through inbound replication. This number is the sum of the bytes of uncompressed and compressed data received during inbound|
Two DCs were isolated (no client or other server activity)
15,000 users were created from script with the minimal attributes populated on one DC
Enabled the connection between the two DCs.
To give an idea of rate of events logged with this level of verbosity:
A Directory Services event log configured to 100 MB in size wrapped in less than two minutes (1 minute 27 seconds). The log contained 195,728 events. Of all events, 189,340 were event ID 1412 (attribute addition). The number of event 1412s per second:
Event ID 1365 (Object creation) was logged 6,312 times in 1 minute 27 seconds.
In one minute, 4,630 user objects were created, consisting of 138,900 attributes) or about 77 objects per second.
An understanding of NTDS performance counters is needed in order to troubleshoot this issue effectively.
Object creations per second is obtained via the following performance counters:
- NTDS / DRA Inbound Objects Applied/sec
- Database adds/sec
- NTDS / DRA Inbound Values (DNs only)/sec
This number includes objects that reference other objects. Values for distinguished names, such as group or distribution list memberships, are more expensive to apply than other kinds of values because a group or distribution list object can include hundreds or thousands of members. In contrast, a simple object might have only one or two attributes. A high number from this counter might explain why inbound changes are slow to be applied to the database.
Attribute creations per second is:
- NTDS / DRA Inbound Properties Applied/sec
Special Condition Frequently Encountered
Repadmin /rehost results in status 8461:
This issue occurs when the GC being rehosted is busy accepting updates for other partitions. The sourcing of writable domain partitions including schema, configuration and domain partition are by nature higher priority work-items than the rehosting of a read-only domain partition.
Repadmin /queue output should show that the request to add the partition has been queued and will eventually be processed. However, sometimes it is necessary to use an alternative method of partition rehost:
- Repadmin /unhost
- Wait for event ID 1660
- Disable KCC connection translation
- Repadmin /add
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