Cross site DAG and CAS

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K

kyury



Hi,

have a couple of questions about auto switch over and split-brain syndroms when working in a cross site situation.

I have 2 AD sites spanning between 2 physical sites - both site's have active users working in them.

In my primary site I have 2 MBX servers and 2 CAS/HUB servers.

In my secondary site I have 1 all-in-one server.

I have configured a DAG between all 3 MBX servers, and CAS array between the 2 servers in my primary site.

Users in the primary site are connecting to the CAS array, and users in the secondary site are connecting to the all-in-one server.

the questions are as followed:

1. Lets say one of my site fails - is there an automatic way to redirect all users in that site to the other CAS server?

2. Lets say that the network link between the site goes down - what will happen to the DAG DB's? I have activated DAC on my DAG (I have 3 server's), so that means the the DB's will not auto mount right? but what happens if the server actualy fails? will it also not auto mount?

Thx!

yuryk
 
B

Brian Day MCITP [MVP]



1. Do you mean external or internal users? Are the internal users located in the same site that just failed? (Then no for them for sure). For external users you would need to update your external DNS records to point to the DR site as part of a Datacenter Failover.

2. If you have a cross-site DAG w/DAC enabled then the site with 1 node will dismount any mounted DBs and not be able to mount any others unless you perform manual operations to force them to mount. I don't understand the second part of your question. If a server fails then you lose communication with it just like if the WAN failed, Exchange won't know the difference.

My posts are provided "AS IS" with no guarantees, no warranties, and confer no rights.
 
K

kyury



Thx for the answers.

Brian:

1. I mean both internal and external users. My internal users are located on a different AD site, and are on the same site that just failed. From what I've been reading I guess that I have to initiate the Set-MailboxDatabase -RpcClientAccessServer to redirect all the users in the failed site to the CAS server in the other site thats working. Is that right? Is there no way to auto redirect them?

2. So what you saying is that all the DB's that are mounted on the servers - in both of the sites (if the network goes down) will be auto dismounted? And I will have to auto mount them manually?

yuryk
 
J

jader3rd



1. There is no recommended way to redirect the Cas traffic. Cas arrays are tied to sites. I have seen some ideas proposed around a hard load balanancer infront of both Cas sites or round robbining, but both are bad ideas that leave you with miserable performance in the normal use case. It's kind of by design that you don't get automatic Cas redirection failover.

2. If the link goes down all of the databases will mount in the primary site (assuming that both of the mailbox servers in the primary site are up). The mailbox server in the secondary site will lose quorum and make sure that databases won't mount on it until it regains quorum.
 
K

kyury



1. There is no recommended way to redirect the Cas traffic. Cas arrays are tied to sites. I have seen some ideas proposed around a hard load balanancer infront of both Cas sites or round robbining, but both are bad ideas that leave you with miserable performance in the normal use case. It's kind of by design that you don't get automatic Cas redirection failover.

2. If the link goes down all of the databases will mount in the primary site (assuming that both of the mailbox servers in the primary site are up). The mailbox server in the secondary site will lose quorum and make sure that databases won't mount on it until it regains quorum.

so what happens to the mounted DB's on the server in secondary site? it will auto dismount to prevent split brain?yuryk
 
N

Neil Hobson [MVP]



Yep, those databases will dismount as the server in the secondary site doesn't have quorum.


"kyury" wrote in message news:93b41a9a-2e33-4548-9a49-b190b7d1739b@communitybridge.codeplex .com...


1. There is no recommended way to redirect the Cas traffic. Cas arrays are tied to sites. I have seen some ideas proposed around a hard load balanancer infront of both Cas sites or round robbining, but both are bad ideas that leave you with miserable performance in the normal use case. It's kind of by design that you don't get automatic Cas redirection failover.

2. If the link goes down all of the databases will mount in the primary site (assuming that both of the mailbox servers in the primary site are up). The mailbox server in the secondary site will lose quorum and make sure that databases won't mount on it until it regains quorum.

so what happens to the mounted DB's on the server in secondary site? it will auto dismount to prevent split brain? yuryk Neil Hobson, Exchange MVP
 
K

kyury



Hi Neil,

Sorry for the late respone.

In that particular case, when the WAN link is down and the secondary site DB is auto-dismounted - what steps should I perfrom to mount it again?

yuryk
 
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