Exchange 2013 CU4

in our config, our DAG consists of only two MB and CAS servers. in the event of a failure of one of the servers in a pair, we'd be running on one leg only.

i was thinking why not add a 3rd server for each MB and CAS so it'd be like a "RAID 5" config. if one server goes down, we're still good. or is there a rule against such configuration?

Hi Reno,

Yes, you can add a 3rd server to an existed DAG, there is no rule against this configuration.

You can refer to the following article to understand how to add a server to a database availability group :

Manage database availability group membership

When you add a server to a database availability group (DAG), it works with the other servers in the DAG to provide automatic database-level recovery from database, server, or network failures. When you remove a server from a DAG, it's no longer automatically protected from failures.

Best regards,

hi, thanks for the link though i know how to add a server to a DAG. just wanna make sure my idea of a "RAID 5" DAG config is workable or not against any good practice.

Hi

Are you using a witness in an alternate site? You wont use it as you have an uneven node majority.

How are you going to store the logs and DB? same drives or separate?

my logs and DB are on same drive. as per best practice on Exchange 2013.

ahh the witness. i think this is why i asked if a 3 node DAG is recommended. the on-premise CAS is where my witness is configured.