Exchange Server down, DAG Databases not coming up


We have 2 sites, each with an Exchange Server 2010, all roles.

This morning the main site went down.

Instead of the 2nd server mounting the database copies, they are all failed or failed and suspended.

How should we get these up? It's basically saying it cant see the other server but that is the whole point of Exchange DAG?
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Chinthaka_ShameeraConnect With a Mentor Commented:

Nope Exchange 2010 Sp1 Supports for the DAC with 2 member DAG with different AD Site.

Datacenter Activation Coordination (DAC) mode is a property setting for a database availability group (DAG). DAC mode is disabled by default and should be enabled for all DAGs with two or more members that use continuous replication. DAC mode shouldn't be enabled for DAGs in third-party replication mode unless specified by the third-party vendor.
Peter HutchisonSenior Network Systems SpecialistCommented:
It may be down to the number of votes. For other node to come up you need at least half of the hosts +1 to be up to allow automatic failover. Do you have a witness server configured? Preferably not one of the 2 two exchange servers.

See this blog:

Nope Site Fail over is not automated.
If you have two AD sites you need to do manual fail over. This will happen when majority lost and 2nd site cannot access the FSW server. please let me know below information.

1) Number of sites ?
2) Number of Database Servers for Each site ?
3) Witness Server Location  ?
4) Witness Server location ?
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bikerhongAuthor Commented:

2 physical sites, geographically separate, different subnets, connected via IPSEC VPN
1 Database Server per site
Witness Server located in HQ site

We've managed to get it all running on DR site now, after manually changing the DAG IP in DNS and rebooting the server.

However during this process the HQ site came back up breifly, so unsure if this had any effect.

i am not so sure what are you talking about removing the DAG ip that you should not to do.
as MS you should have DAG ip by each sub net you have in the DAG properties.
bikerhongAuthor Commented:
I never said anything about removing the DAG IP.

the DAG object has 2 IP Addresses associated, one on each subnet, primary being the HQ IP.

All I did was change the DNS so it reflected the DR DAG IP instead if that makes sense.
Ar you Referring by DAG IP is Server FQDN at DNS ?If yes its fine.

Check if you have enable the DAC on the DAG. If you have enabled the DAC, you should not face any problems if HQ Servers come online. Otherwise you will face split brain situation.

bikerhongAuthor Commented:
It says here:

DAC mode shouldn’t be enabled for 2 member DAGs where each member is in a different AD site
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