Comments on: Exchange 2010 Database Activation Coordination (DAC)

By: Elan Shudnow

Elan Shudnow — Tue, 07 Feb 2012 17:07:13 +0000

If you perform step 5 and DAC is enabled on the DAG before you simulate the failure, when the Primary Site comes back up, those servers will not mount databases since DAC is enabled and cannot contact the rest of the DAG Servers.

By: kysellbook

kysellbook — Thu, 02 Feb 2012 22:03:14 +0000

If I move all the active databases from the primary datacenter to the standby datacenter first, then perform the following steps below. Do you think the mailbox servers in the primary datacenter will mount the database, assuming that the DAC is enabled?

(1) Stop the DAG in the primary site

(2) Activate the DAG member servers in the standby site. This step will evict all the nodes in primary site. Also it will stop and disable the cluster service on the mailbox servers in the primary site.

(3) Transfer the file witness server from primary datacenter to the standby datacenter.

(4) Suspend the database copy replication between primary datacenter and standby datacenter.

(5) Sever the WAN link between primary site and standby site.

Primary Datacenter: 4 mailbox-role servers and one witness server
Standby Datacenter: 2 mailbox-role servers and one witness server
One DAG spans two datacenters: primary and standby

We are trying to simulate the site failure recovery procedure as much as we can, without any data loss.

I am not able to find any information about this type of simulation on the Internet. I would really appreciate if you can provide me some insights.

By: Elan Shudnow

Elan Shudnow — Thu, 29 Dec 2011 16:28:04 +0000

There's no such thing as 2 node DAGs? Sure there is, create a DAG and add 2 Mailbox Servers into this DAG. You now have a 2-node DAG. And in Exchange 2010 RTM, if you only had 2 nodes (2 Mailbox Servers) in a DAG, you could not enable DAC since DAC required you to have 3+ Mailbox Servers within this DAG.

And there's no such thing as non multi-site DAGs? I already explained myself that with Exchange 2010 RTM you can enable DAC when you have 3 Mailbox Servers in a DAG as long as one of those DAG members is in a different site. You cannot enable DAC if your DAG members are all in the same AD Site. Hence why you can't enable DAC in a non-multisite DAG.

By: Akul Jay

Akul Jay — Thu, 29 Dec 2011 10:51:34 +0000

I meant 'Non-Multisite DAGs'…

By: Akul Jay

Akul Jay — Thu, 29 Dec 2011 10:46:59 +0000

Elan,

Though people like us are grateful to you for this and other articles, sometimes, you state things in confusing way. Why say "DAC should not be enabled for 2 member DAGs or multi-ste DAGs in Ex 2010 RTM" since there is no such thing as '2 member DAGs or multi-ste DAGs in Ex 2010 RTM.'. There was absolutely no need for that advisory!

By: Ashif

Ashif — Mon, 16 May 2011 10:10:13 +0000

Hello Elan,

In my Environment i have implemented two Mailbox server in Primary site and two in DR site, FSW is hosted by CASHT01 server in primary site and Alternate FSW in hosted in DR CASHT03 server. In my case what will happen if primary site gose down ? All DB will mount to DR autometically ? Will Alternate FSW will be act as voter node in case of primary FSW fail ? How the mejority and FSW will count if my primary site goes down?

Ashif.

By: Brendan

Brendan — Fri, 25 Mar 2011 00:09:08 +0000

Servers cannot belong to more than one dag. For 2 DAGs you have to have 4 servers and 2 WFSs minimum.

What happens in a 4 server 1 WFS DAG, when one server cannot communicate with a server that holds a primary database? Does this server tell the PAM to move the active database to another server? If there is only 1 server which cannot communicate with a primary database server I would hope it does not cause it to failover.

Where does the alternate witness file share come into place??

Thanks for your help,
Brendan

By: ZAHIR HUSSAIN SHAH

ZAHIR HUSSAIN SHAH — Tue, 02 Nov 2010 10:44:53 +0000

Hi Elan,

Leeme first tell you that I’m the biggest fan of your articles, because the way you describe scenario and their solution, is simply commendable!

I have some questions, for your kind attention:

Scenario: I’m designing a Exchange 2010 SP1 based Messaging design, where we want DR setup to be available for us using DAG.

All users will connect to Primary Datacenter, and only in the event of disaster happens, then all users will move to the DR site.

We are sharing the same name space for both data centers, HO.ABC.COM on both datacenters.

Primary Data Center will contain:
2 Nodes for CAS / HUB Exchange 2010 SP1 on Windows Server 2008 R2
2 Nodes for Mailbox Servers Exchange 2010 SP1 on Windows Server 2008 R2
Witness Server would one of the HUB Server in Primary Server

Questions:
1) Can we have 1 witness server and two Mailbox Server in the primary site, and only one Mailbox/CAS/HUB Server in the DR site?

2) In this scenario what name space structure do you recommend, either shared name space or different name space?

3) In the event of complete Primary Datacenter failover, and where I have only single server in DR site containing Exchange 2010 SP1 Mailbox/CAS/HUB, do I also need to create standby Witness server to keep required votes in the DR for mounting databases?

Looking forward to hear from you soon;

Zahir Hussain Shah

By: Elan Shudnow

Elan Shudnow — Sat, 16 Oct 2010 13:56:46 +0000

The guidance to get around this is have 2 DAGs; Site1DAG and Site2DAG. For Site1DAG, you'll have the majority of servers for Site1DAG in that site including the FSW so if WAN goes down, users can still work since the majority of the servers are in Site1 and it's only the failover servers for that DAG are in Site 2. For Site2DAG, you'll have an entirely new DAG with the majority of servers for this new DAG in Site2 including the FSW for this DAG (since each DAG has its own FSW). The failover servers for this DAG would like in Site1. If the WAN link goes down, because the majority of the servers for this DAG are in Site2, Site2 users will still be able to work.

So yes, you need 2 DAGs if you want to prevent the WAN link bringing down 1 site.

By: Jorge Salinas

Jorge Salinas — Sat, 16 Oct 2010 08:44:52 +0000

Dear Friends,

I have a two node DAG, each Exchange 2010 Server Mailbox is located in a different Active Directory Site. Each Exchange 2010 Mailbox has its own mailbox database and each one of them serves local users. (In short, I have active users in both sites). FSW is located in Site 1

Anytime I have a WAN outage, The Exchange Server located in Site 2 will loose contact with ths FSW and will dismount its database… so users located in Site 2 cant work.

I would like to know what should I do to enable service on Site 2

I really hope you can help me with his one..!

Jorge Salinas