April 24, 2009 at 5:54 am
Two Node Shared Quorum to 3 Node MNS Fileshare Witness
Has anyone got any ideas on how to achieve this.
We are implementing a DR Site and wondered if this was the best way to appraoch adding a 3rd node down at the DR site.
Currntly sitting on 2 x 2003 SP2 SQL 2005, EMC Clariion Backend.
April 26, 2009 at 12:13 am
First off, remember that HA is not DR. Microsoft Clustering provides a HA solution, not a DR solution.
It also depends on what you classify a disaster and what your qualifications for disaster recovery are. Is your second site running hot, warm or cold? Is it an automatic or manual failover?
Majority Node clusters aren't that much different to quorum based clusters, except - there is no quorum. Basically you are talking about building a geo-cluster - geographicall distributed. That's fine, as long your WAN can meet the reponse time for the cluster heartbeat. One big question, and this could pretty much be a show stopper, do you have a CLARiiON at both sites? If so, how are the configured? same fabric? are you using MirrorView to replicate between arrays? etc... Then you have issues such as which array is the master in a one direction replication model.
We've recently setup a DR site for the government agency I work for. It is a (mostly) cold site with a disaster being declared by people and manual processes to fail over. This is DR, not HA. We use a Symetrix class array with SR/DF. At the second site, we have clusters (different names) with the same configuration as at the primary site. SR/DF replicates LUNs and at the DR site they are read-only and unmountable.
If you want more information, feel free to message me. This is quite a large topic and lots of thought needs to be put into the design.
Cheers
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Andrew Hatfield
April 28, 2009 at 5:44 am
Thanks for the reponse.
We term a disaster when our main London site is down.
Yes we are using Clariions at both sites using Mirrorview /CE with Mirroview /S with London being the Primary.
We are told that we can only use SQL MNS Cluster with Mirrorview.
So is there a set procedure to change a two node Quorum cluster to a three node MNS cluster?
April 30, 2009 at 11:41 pm
I'm not sure how MirrorView works, but I'd imagine it is similar to SR/DR. With SR/DF, the second array has the LUNs locked and can only receive the replicated updates from the primary array.
You can zone the LUNs to a host, but they appear as inaccessible. When you declare a disaster and failover to your secondary site, you break SR/DF replication and then the LUNs at the second site become available and you can write to them.
The EMC solution is to setup identical clusters at your DR site that are down. When you have a disaster, break replication and turn those clusters on - viola, data is accessible and applications can connect.
As for changing from Quorum based clustering to Majority Node Set, I believe that is a reinstall.
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Andrew Hatfield
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