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Two DAGs In same Exchange Environment.

Currently we have two nodes of Exchange 2016 in DAG mode and mailbox database are resides on NTFS formatted drives.  Now we are planing to add another two Exchange 2016 nodes will create separate DAG in same environment but will set ReFS file system on this DAG and Mailbox Databases will resides on ReFS formatted drives.

Q1.  Is there any precautions for adding second DAG in same environment?
Q2. Creating second DAG in same environment is best practice or not?

Guys please suggest.
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System Engineer
What you are planning is perfectly fine as there is no problems with having multiple DAGs. ReFS are new and just recently supported for 2016 for only the logs and database files so you shouldn't have a problem but I always steer away from the newest thing but totally supported. Make sure you have the proper updates installed if you are using server 2012.
Muhammad AsifSenior Solutions Architect


Hi Sean,

I'm following the Microsoft's preferred architecture (PA) for Exchange 2016 and according to their recommendations I have:

Windows Server 2016 Standard Edition (x64)
NTFS formatted OS drives.
ReFS formatted storage drives for databases and logs.
GBT as format style.
64K block size.
Disabled integrity streams.


When I try to create a mailbox-database, the Exchange shows a permissions warning message which is given below with a separate heading. It is also worth mentioning that the databases are created fine in the Exchange but I still need to know the root cause of this warning, as the permissions in place are absolutely fine.

Error Description:

There was a problem creating directory "D:\Program Files\Microsoft\Exchange Server\V15\Mailbox\REFSDB01" on server "hostname.domain.com". In order to ensure that the Exchange data is kept secure, please create the directory, if it does not already exist, and configure directory permissions so that "SYSTEM" and the local "Administrators" group have "Full Control" for the folder, subfolders, and files. It is recomended that permission inheritance be broken so that only "SYSTEM" and "Administrators" have access to the directory.


Can you guide on the ReFS formatted drives? This problem seems to be coming due to this format. When I use NTFS, Exchange does not show such a warning. Can someone guide me on the permissions required or the pre-requisites for ReFS that I might have missed? BTW, I have checked the permissions on drives both NTFS and ReFS drives have the same permissions.