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EXCH 2010 DAG having 4 memebers

Posted on 2014-03-24
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Last Modified: 2014-03-31
I currently have 2 servers in the DAG A and B, and will be adding 2 more Mailbox servers to the DAG, C and D
My question is right now the dbs that are on the 2 servers in the DAG (A and B) have copies of each of their DBS on each. Now I will be adding 2 more MB servers to the DAG,(C and D) but these 2 will have different dbs than are on the other 2. Is it ok to have copies of dbs on the original 2 MB servers A and B between them and then have the copies of the DBS from the 2 new MB servers C and D between them?
So basically A and B share copies and C and D share copies...
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Question by:vmich
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by:EEhotline
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That is totally OK, though if you have enough space, you can make 2-3 copies of a db instead of 1.
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by:vmich
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Yes well I figured down the road once there is more space purchased for the san, then we could add more copies...
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by:Amit
ID: 39951494
It depends what is your business requirement. Practically one copy is enough, if you have regular backup running. Focus on

Redundancy: DB Copy, Server, Power Supply, SAN
Resiliency: Server and Site
Recovery: Backup strategy.
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Adam Brown earned 250 total points
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Honestly, you may want to have a separate DAG for each pair, since the failover scenarios with what you have described could cause some problems. With two database copies on half your nodes in a single DAG, you could end up with some really messy failover situations. For instance, if you lose two servers in the DAG and the FSW setup to have the odd numbered vote, you could potentially cause a cluster shutdown for all databases, even if only one server in each pair shuts down. By way of explanation, let's say you have Copy a and b on servers 1 and 2, and copy c and d on 3 and 4, with FSW on 5. If you have two dags, you can have an additional FSW (6), but with a single DAG, you could lose server 1, 3, and 5 and even if server 2 and 3 are capable of running, the cluster will fail and you would have to perform a cluster recovery. If the same happened with two separate dags, one dag would be unaffected while the other would fail (because it lost over half its nodes).

If you have a DAG, it's always best to make sure there are as many database copies as there are nodes in the DAG.
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by:vmich
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