Comments on: New DAG Activation Preference Behavior in Exchange 2016 CU2 is Good News for Some

By: Suzy Semanco

Suzy Semanco — Wed, 22 Apr 2020 23:25:34 +0000

I’m 99.9% sure I’ve figured this out. The automatic failover/back of the databases occurs at the time of the last start of the Microsoft Exchange DAG Management service on the PAM server. If the Microsoft Exchange DAG Management service start at 10:25:45PM, then that is when databases will automatically fail back to their home servers.

So, this gets a little crazy as I work through 4 servers applying patches. The PAM moves to another server when I put one into maintenance mode, etc.. But, once maintenance is done the PAM goes back to the preferred server and this information is useful when I do other maintenance.

Thanks!

Suzy

By: Suzy Semanco

Suzy Semanco — Wed, 08 Jan 2020 14:39:17 +0000

Hi Paul, something I’ve noticed is that the automatic failover time changes during our patch/reboot weekend. Do you know “what” determines the automatic failback time? After every reboot weekend I have to “figure out” when the databases will automatically failback to avoid having them do it while I’m putting a server into maintenance mode. I like to fail the databases manually through EAC first, then put the server into maintenance mode once all the databases are moved off of the server. I know, it seems a bit OCD but I prefer doing it this way.

It doesn’t seem to be the Exchange servers themselves because I’ve done other changes like CU updates and the time frame doesn’t change. It only seems to change during patch/reboot weekend. It’s got to be the witness server or the domain controllers? I have eyes on when the witness server reboots but that doesn’t seem to be it either..

It changes every month but I can’t pin down which server reboot is reseting the time that the automatic failovers happen. Do you know?

Thanks!

Suzy

By: itay

itay — Wed, 27 Mar 2019 10:23:06 +0000

Hello Paul,
i deployed a new Exchange 2016 DAG. it contains 10 mailbox server and 30 DB’s.
each mailbox server has 3 active DB’s and 6 copies (two passive copies for each database).
i noticed that, wherever the PAM is on, the MICROSOFT EXCHANGE REPLICATION service is restarting every 20 seconds repetedly. that causing the active databases on the mailbox holding the PAM to be down and unknown every 20 seconds.
i am getting a “watson report” event in the application event log.
can you give me any direction for this issue?
thank you,
itay.

By: Paul Cunningham

Paul Cunningham — Wed, 14 Mar 2018 19:24:04 +0000

In reply to Brandon Stevens.

You should not be restoring the failed server to a previous point in time. That is not a supported recovery method.

This is the correct and supported approach:

https://www.practical365.com/exchange-server/recovering-a-failed-exchange-2016-database-availability-group-member/

By: Brandon Stevens

Brandon Stevens — Wed, 14 Mar 2018 17:50:45 +0000

Forgive the basic question as I am new to Exchange 2016. I have a DAG established. 1 of my servers went down due to Microsoft update and we were unable to strip out the bad update. We restored the server to 3 days prior
Question:
When we power on this server, will the DAG automatically replicate or do I need to manually reseed using power shell? Also, the value for Activation preference number, does this have any bearing on which DB is the “master copy”. One of my concerns is that the server that failed was the primary when failover occured. Does this value indicate which is primary copy?

Thank you and I appreciate any info
Brandon

By: Scott

Scott — Mon, 20 Mar 2017 16:18:18 +0000

Hi Paul,

It looks like MS now recommends to set an infinite time so you don’t have to recycle the replication service.

https://blogs.technet.microsoft.com/exchange/2016/06/16/dag-activation-preference-behavior-change-in-exchange-server-2016-cu2/

Set-DatabaseAvailabilityGroup -PreferenceMoveFrequency ([System.Threading.Timeout]::InfiniteTimeSpan)

By: Paul Cunningham

Paul Cunningham — Wed, 09 Nov 2016 00:37:27 +0000

In reply to Harry. Why do you want to disable it during server maintenance?

By: Harry

Harry — Tue, 08 Nov 2016 16:15:19 +0000

Hi Paul,

Another great post. Quick question, what is the easiest way to temporarily disable auto redistribution DAG, say, at server maintenance windows, etc. ?

I see my DAG -PreferenceMoveFrequency is set by default for one hour.
I see this option:

Set-DatabaseAvailabilityGroup “dagname” -AutoDagAutoRedistributeEnabled ($True or $False)

Will this serve the purpose? Do we need to restart Microsoft Exchange Replication service ( if it requires On PAM only or on all of DAG member servers?) as well after the switch is turn off?

Thanks,
Harry

By: Jan Dye

Jan Dye — Tue, 09 Aug 2016 13:18:37 +0000

Is there a particular event that is written to the application log when databases are moved around? Thanks for this great feature!

By: Paul Cunningham

Paul Cunningham — Mon, 20 Jun 2016 03:54:23 +0000

In reply to Kiran Ramesh. No, it won't override anything else.