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Sunday 21 August 2011

Exchange 2010 MountDial

The setting is set per server. You can determine the value on your server by typing the following cmdlet:

[PS] Get-MailboxServer | FL Name,AutoDatabaseMountDial

MountDial determines if a passive copy of a DAG can automatically come online based on how many log files being copied to it. If you run the above command, you will see one of several values for AutoDatabaseMountDial including:

  1. BestAvailability
  2. GoodAvailability
  3. Lossless

These mean the following:

BestAvailability

If you specify this value, the database automatically mounts immediately after a failover if the copy queue length is less than or equal to 12. The copy queue length is the number of logs recognized by the passive copy that needs to be replicated. If the copy queue length is more than 12, the database doesn't automatically mount. When the copy queue length is less than or equal to 12, Exchange attempts to replicate the remaining logs to the passive copy and mounts the database.

GoodAvailability

If you specify this value, the database automatically mounts immediately after a failover if the copy queue length is less than or equal to six. The copy queue length is the number of logs recognized by the passive copy that needs to be replicated. If the copy queue length is more than six, the database doesn't automatically mount. When the copy queue length is less than or equal to six, Exchange attempts to replicate the remaining logs to the passive copy and mounts the database.

Lossless

If you specify this value, the database doesn't automatically mount until all logs that were generated on the active copy have been copied to the passive copy.

BestEffort

This will mount no matter the copy queue length. Be careful with this setting as you could loose a lot of mailbox data!

 

To manually switch from passive to active type the following cmdlets:

[PS] Move-ActiveMailboxDatabase DB4 -ActivateOnServer MBX3 -MountDialOverride:None
As the MountDialOverride property is set to ‘none’ whatever is currently set (probably the default) remains. 
The default on my server is GoodAvailability. So, replace none with one of the three options listed above to change this.
Read an earlier post regarding DAGs 
Ref.

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