Environment - Exchange 2013 SP1

1 DAG 2 x Physical locations separated by a WAN link (high speed) DAC mode is enabled

1 AD site on a stretched subnet between the 2 sites

Site 1

3 CAS (Server CAS01 is also file share witness, CAS01 is also VM replicated to Site 2 for Backup & DR)

2 MBX both primary with activation preference either 0 or 1

Site 2 (DR)

1 MBX Server with passive copies of all mailboxes

Scenario

Site 1 has a power cut for an indefinite amount of time so DR needs to be invoked and mailboxes must be mounted at DR

CAS01 is brought online at Site 2 so the FSW is back

MBX03 is still online at site 2

what do I need to do to mount databases on MBX03 considering quorum was lost as site 1 went offline?

stop-databaseavailabilitygroup?

restore-databaseavailability

Hi KingMT,

Thank you for your question.

By my understanding, if site 1 is offline, DAG will not work for mailbox high availability. Because the number of DAG member are even, which is MBX03 and FSW on CAS01 copy. The function of failover will not work. We could refer to the following link:

https://technet.microsoft.com/en-us/library/dd979799%28v=exchg.150%29.aspx

We could manually mount databases, which is passive copies of all mailboxes. So we didnt use the command of stop-databaseavailabilitygroup and restore-databaseavailabilitygroup.

If there are any questions regarding this issue, please be free to let me know. 

Best Regard,

Jim