Theoretical question - Hyper-V / Server / SAN replication - Disaster recovery.

At the end of the year, we are to replace some servers for a customer. They are thinking about disaster recovery and damage limitation if one of their buildings should flood, or go up in flames etc., and because of this they are going to have a physical server and SAN in their main building and a duplicate physical server and SAN in a satellite office, both of which are connected via a fibre link and will replicate data.

The "plan" is that one server/SAN will be the primary, and the other will act as a backup - the two will replicate. So far so good - users will still be able to log on and access data.

Now, my question is this. Supposing, the fibre link between the two buildings goes down or gets cut (as one recently did at this site - by a careless contractor!). If one combination of server/SAN is serving the main building and the other server/SAN is serving the satellite office, what happens when the fibre link is restored?

The physical servers will have 4 Hyper-V guests, 3 of which will have SQL applications such as CRM, SharePoint, Document management etc....

My concern is will one set of data overwrite another, or will the SQL databases be able to "merge" any differing records with the same record IDs etc?

I've never done anything like this before and I just want to understand what would happen in this scenario.

LVL 17
Chris MillardAsked:
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Ideally for a workable DR solution, all writes should go to the Primary location, hence the primary gets replicated to secondary and in the event of failure.

All primary site activities fail over to the secondary, I would just have 1 way replication from Primary to secondary using the storage vendors replication software, supposedly the MS SQL server LUN(s) are physcal RDM's which can be replicated by the storage as well.

Note that you *will* need to reverse the replication in order to fail-back the solution.

Hence my best advice is to talk to your storage vendor regarding what available solutions they have [VSS aware snapshots, replication], based on available functionality they will suggest a best fit solution.

Out of further interest what storage do you have in use?

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Chris MillardAuthor Commented:
At the moment, nothing yet - but it looks like it's going to be a Dell SAN solution.
I'd speak to a storage specialist at Dell. You can peruse some of their offerings here.
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