nashiooka
asked on
Exchange 2010 DAG stretched to 3 data centers?
I need information on hosting a DAG stretched across 3 data centers. I haven't found any reference scenarios yet. I'm actually trying to combat this proposal! The scenario would be something like:
- Data center 1 located in India replicating databases to servers in data center 2 in California.
- Data center 2 in California hosting the quorum and its own active databases replicating to Data center 3 in New York
So India's databases are replicated to California but California's are replicated to New York.
The first detraction I can think of is, and this is if I understand correctly; if the WAN link goes down between India and California the India servers will lose quorum and there will be an outage?
Let me know what you guys think. Thanks.
- Data center 1 located in India replicating databases to servers in data center 2 in California.
- Data center 2 in California hosting the quorum and its own active databases replicating to Data center 3 in New York
So India's databases are replicated to California but California's are replicated to New York.
The first detraction I can think of is, and this is if I understand correctly; if the WAN link goes down between India and California the India servers will lose quorum and there will be an outage?
Let me know what you guys think. Thanks.
Ben Hart
Depending on where the Quorum is located, yes. The way I'm understanding the above situation yes at least two servers need to be able to communicate with the Quorum if any one link goes down.
Which mean, IMO that each site needs two WAN links.. one for production and the second for Quorum.
What is your ultimate Goal from this design? Then we can suggest what you need.
I have seen this done and it doesn't work in the way that people think at all. I have just finished removing such an implementation because it failed to failover as designed.
If you need to protect three sites then the best option is to have at least two, preferably three DAGs, one for each location, with the replica in another site.
I would be very surprised if you were able to get two independant paths for the internet in India. By that I mean completely seperate telcoms company, different exchanges, different technology etc. Most of it goes over the state telecom company in most locations.
Simon.
If you need to protect three sites then the best option is to have at least two, preferably three DAGs, one for each location, with the replica in another site.
I would be very surprised if you were able to get two independant paths for the internet in India. By that I mean completely seperate telcoms company, different exchanges, different technology etc. Most of it goes over the state telecom company in most locations.
Simon.
ASKER
I'm not too keen on this idea myself, I'm actually looking for information so I can disqualify it.
The goal of the design is to provide site failover capability for both India and California. India to CA and CA to NY. Day-to-day no active users in NY. The sites are connected in an MPLS network with dual links. at this juncture I'm not concerned with the inderlying telecom infrastructure in India.
My thinking is this is technically possible, but hard to support. Without reference designs I'd have to develope different procedures for site failovers. When we experience cluster issues I don't know how everything will react. An example: let's say the CA site is destroyed by Earthquake. I think the other sites will stay up because they still have quorum, and I should be able to failover the DB's. That said I will probably have to reestablish the witness to the alternate which will likely cause downtime in India.
I'm not entirely confident in any of this, so please poke as many holes as you can.
The goal of the design is to provide site failover capability for both India and California. India to CA and CA to NY. Day-to-day no active users in NY. The sites are connected in an MPLS network with dual links. at this juncture I'm not concerned with the inderlying telecom infrastructure in India.
My thinking is this is technically possible, but hard to support. Without reference designs I'd have to develope different procedures for site failovers. When we experience cluster issues I don't know how everything will react. An example: let's say the CA site is destroyed by Earthquake. I think the other sites will stay up because they still have quorum, and I should be able to failover the DB's. That said I will probably have to reestablish the witness to the alternate which will likely cause downtime in India.
I'm not entirely confident in any of this, so please poke as many holes as you can.
This is exactly what I have just undone, because it didn't perform as expected in a failover scenario. Too many variables.
If there are no users in the "central" site that makes things very easy.
Deploy two DAGs, one for each site. The passive is on one of two servers in the central site.
The active servers could be one or two, depending on the load.
The FSW would be in the LOCAL location, so if the link fails between the central site and the satellite location, the DAG stays up.
In the event of a site loss then the procedure from Microsoft for dealing with data centre loss is followed.
Very simple to understand, very predictable failover in the event of almost all scenarios.
Simon.
If there are no users in the "central" site that makes things very easy.
Deploy two DAGs, one for each site. The passive is on one of two servers in the central site.
The active servers could be one or two, depending on the load.
The FSW would be in the LOCAL location, so if the link fails between the central site and the satellite location, the DAG stays up.
In the event of a site loss then the procedure from Microsoft for dealing with data centre loss is followed.
Very simple to understand, very predictable failover in the event of almost all scenarios.
Simon.
ASKER
I agree I would rather do 2 DAGs. Can you add any specifics to the problems in the 3DC design. I'm looking for Ammo to get that off the table.
Let me know. Thanks.
Let me know. Thanks.
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ASKER
Thanks very much for your input. It's valuable info. I am having a conversation with MS tomorrow, if I have anything to add thereafter I will let you know.