Exchange 2012 DAG

I have a exchange server running as VM in Vcenter server with three drives. C has OS, E has Exchange installation and F has DB and log.
I have setup second Exchange with MB and CAS (I wont be using CAS for HA) with same amount drives. During the installation it automatically added DB to default drive which I need to move from E to F.
I have already configured and stage cluster computer account with required permission and disabled it.
Before I add any member and witness to DAG would like to clarify that last part of the DAG process, which is CONFIGURING DATABASE COPIES. Is it important to create to DB copies for successful replication or it should sync with secondary server without copy.
IF the DB copies are needed, would be copies be same size as mailbox database. Is it recommended to create and stage separate drive on both server for creating DB copies.
My existing drive for DB and log has 40% of space and do not want to use same drive for DB copies and I presume, if I use different drive letter for one server I have to use same on second one too.
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pchettriIT DirectorAsked:
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StuartTechnical Architect - CloudCommented:
If you don't want to use the same drive for a live DB and DB copies then you will have to separate the databases to dedicated drives. Drives should be the same on each server and the copies will use the same path

Eg Server 1

F: - DB1 & Logs Active
G: - DB2 Copy

Server 2

F: DB1 Copy
G: DB2 & Logs Active
Jeff GloverSr. Systems AdministratorCommented:
As Stuart indicated, For Mailbox servers in a DAG, they need the exact same Drive configuration for mailbox databases and logs. When you add a Mailbox Copy to a DAG, you only specify which mailbox server it is on, It will automatically make the copy for you using the same drive letters. You cannot change that.
 Yes, the databases will be the same size. The logs can vary a little but will be close.
pchettriIT DirectorAuthor Commented:
so I would need to have double the space for database copy, which is not mentioned in any of the pre-requisites. This should have been critical piece of information before DAG setup.

I wanted to use same drive if there are not performance hit and same space requirement as primary database
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Jeff GloverSr. Systems AdministratorCommented:
I think I get what you are saying. It is common knowledge though. You need drive space to accommodate the databases. If you do not have the space available, do not make the DAG. Or, as long as you have the same size drives on both servers, just Add both to the DAG and make a copy of the first Servers mailbox database. Don't use the second one. In fact, once the DAG is setup, you can probably just remove it.That is, unless you need 2 Mailbox databases due to the number of users.
pchettriIT DirectorAuthor Commented:
Sounds like copies would three times the size of mailbox database. 1) existing database on main server 2) database copy on main server 3) replication db copy on DAG secondary server.


None of the DAG setup article this key pre-requisite for setting up adequate hard drive space before planning DAG.





Also, the second exchange I installed picked up the default installation drive E as databased repository. Is it alright to delete this location and point the default database location to F. By the way, does it even use default DB location or it is only suppose to use replication and copied database from primary server or it would require both mounted databased and copied database it the secondary server, in which case the space requirement would be 4 times the primary server.


1) main DB on primary server 2) database copy on primary server 3) Mounted db in secondary server 4) and replication and copied DB in secondary server.
StuartTechnical Architect - CloudCommented:
You would have your main DB on server one then your copy on Server 2. You cannot have a copy on the same server as the active (through the DAG function anyway!)

So following on from the above you would have to only provision the same storage as server one on the second server.

You can delete the database created on server two if you have no use for this then ensure your have your DB/Log drive connected ready to hold the copy

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StuartTechnical Architect - CloudCommented:
Just to clarify the steps to take

Delete database on server 2 & delete database & log files
Create F drive on server 2
Ensure database and logs reside on F drive on server 1
Create DAG
Add server 2 to DAG members

You will have your active database with logs on server 1 (F) and the copy will automatically be created in server 2 (F)
pchettriIT DirectorAuthor Commented:
Considering, I already have F drive on server2 I just have to make it member of DAG and it would be automatically replication. That means no need of creating separate db copy for replication to second server.
StuartTechnical Architect - CloudCommented:
Correct just add server 2 as a member and within a short while the DB will transfer
Jeff GloverSr. Systems AdministratorCommented:
Well, you have to add the server to the DAG and then make the database copy. It is 2 different steps but they can be done one after the other
pchettriIT DirectorAuthor Commented:
Can I use the same drive for database copy.  On F drive I have about 65% free space and I am adding additional 25% of virtual disk to increase the size. I do not want to create separate drive as the second server which is suppose to be the physical server does not have much option to increase beyond the 70% free space, therefore, I am trying to avoid making another partition. Further, on existing VM it really does give any IO gain, if I am using different drive letters created out of same physical LUN.

What should be the recommended free space on drive before I plan to prepare DB copy for DAG. Also, is it necessary to have second network for DAG or I can single network?
StuartTechnical Architect - CloudCommented:
You could but then what would be the point, a DAG is supposed to give you resilience however your introducing a single point of failure by placing them on the same LUN

 The recommended size would be the same as your active, which you will of worked out using sizing calculator. Thin provision this is your worried about using a huge chunk of space initially although you won't get the best write times it would mean you don't have to loose ###gb to start with

For the DAG networks I always split them, Not only is it recommend it helps keep the DAG network view tidy, out can then disable replication on the 'MAPI Network'
pchettriIT DirectorAuthor Commented:
I did not understand the part that explains -

Thin provision this is your worried about using a huge chunk of space initially although you won't get the best write times it would mean you don't have to loose ###gb to start with

I have a thick provisioned disk (vmdk) but the I am still using the same LUN from netapps which is presented as ISCSI disk even if I create different disk.  So logically creating different disk is not improving IO performance like real physical drive, which I why the easier option for me is to stick with single drive.
StuartTechnical Architect - CloudCommented:
So if the iSCSI LUN fills or becomes corrupt you loose your data.. What I was getting at was if you create an additional iSCSI LUN and present this to your secondary server (ideally this will be on a different Netapp) then you will keep the resilience. Also if you thin provision the second LUN you will only use what is written which will help your worry about using so much storage
pchettriIT DirectorAuthor Commented:
My second member server on DAG is physical server independent of virtual environment does still need additional iscsi
StuartTechnical Architect - CloudCommented:
Ok that's good then :)
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