Geographically Dispersed Clustering with Clariion

Thanks to Ira Pfeifer for jump starting this topic…I would’ve hit this subject eventually as this has been a rather frustrating experience that I’ve gone through over the years. One of the things that I’ve been pushing for many, many years at EMC is to develop a “GeoSpan” equivalent product for the Clariion environment. In my opinion, our main target audience for CX arrays is the Windows server environments so it seemed like a logical progression for the GeoSpan product to release a similar product for the Clariion line. Symmetrix has SRDF, Clariion has MirrorView. Seemed like a no-brainer to me.

The first sign that this was NEVER going to happen was the name change from GeoSpan to SRDF/CE…SRDF = SYMMETRIX Remote Data Facility so it would’ve been silly to name a product “SRDF anything” if we had plans to incorporate the CX arrays. Next sign was the level of resistance from product management. The PMs kept ignoring my pleas and finally, they asked that I provide a business case scenario showing the market for such a product…this was management’s way of politely telling me to go away. They were fully aware that I was a technical resource and it would be unlikely for someone like myself to provide the necessary logistical information to pursue this further.

Unfortunately for them, I actually do have the vision and desire to see such a thing through and could not be swatted down by some menial paperwork. I found a dozen different customers that have requested exactly this type of product and I submitted a pretty decent case to the different product groups. This got some attention and the developers from the MirrorView team were engaged by the SRDF/CE team to research the feasibility for such a software product. The outcome was that the MirrorView APIs were not capable of handling the types of commands necessary for a GeoSpan equivalent product and it would require a total rework of the MirrorView coding to make this functional. In the end, this idea was rejected even though this is really something we should be providing to our customers.

With that said, it is still possible to setup a geographically dispersed cluster using Clariion with MirrorView with Windows 2003. One of the main reasons why we were told that MV/CE (my name for the SRDF/CE equivelant for MirrorView) couldn’t be done was that MV couldn’t handle the quorum arbitration needed to support a geocluster. If you use a MNS quorum, there’s no need for MV to get involved with the quorum arbitration. You could build a MNS cluster and then create a generic script or application resource to control the MirrorView failover. You would create your physical disk resources and make then depend upon these generic app/script resources and voila…you now have a geographically dispersed MirrorView cluster. If you’re not familiar with NaviCLI commands, I’ve been told that you could contact EMC professional services to help you develop these scripts…some customers are actually doing this today in their environment. 

I spent a little bit of time trying this last week and I successfully setup this type of configuration in my lab environment so I know that this is possible. Now whether or not such a thing would be supported…from an EMC perspective, you would need to submit an RPQ for support from EMC. For MSFT support, this would need to pass HCT testing and submit it to MSFT for review. I do not think there are currently and MirrorView clusters in the Windows Catalog yet.

Another possibility for the Clariion environment would be to use NSI’s GeoCluster or DoubleTake to create host-based mirrors over IP. This is something I plan on testing myself in the next couple of weeks. Stay tuned for those updates.

5 thoughts on “Geographically Dispersed Clustering with Clariion

  1. Very interesting topic !
    I am a big fan of geo-clustering, and have indeed seen this. There are indeed people out there who are running this (this = scripting and MV).

    some tips if you are planning of testing this:

    1) if you use MNS cluster, ensure you install a file-share-witnes as your 3rd node (to maintain majority in your cluster)

    2) if you are scripting your MV commands, ensure your physical disk resource is dependent on the script, this way your script executes first when coming online (after a failover) and does all the MV commands prior to the disk itself coming online.

    if you do not do 2, then cluster is trying to online your disk while the MV commands have not executed yet. Your Physical disk resource will fail, and (depending on settings) this might cause a failback.

    MV/CE… good name for it John, I am definitely going to name it that way !

  2. Hello John,

    I’ve found your blog very useful but I want to understand one of your points a little better.

    I want to understand the details surrounding the quorum abitration issue that you highlight with MirrorView. Can you elaborate?

    What does SRDF/CE do to get round this issue that MirrorView cannot?

    Any further information you can give would be very much appreciated.

  3. I ran into a business case which would have benefited greatly from an SRDF/CE type solution for the clariion. This with a project associated with EMC. The client had 6 SQL geo clusters using MirrorView to replicate the data LUNs to another DR site. They had a need to shift the SQL processing to the DR site. Even though it was the DR site, they had not developed a process to perform such an operation. I was part of a team to develop the switchover process. This required hundreds of manhours to develop and test the manual steps to “freeze” the SQL processes, allow replication to stabilize and then run through the commands to break and reverse the mirror replication, and bring the SQL servers on line.
    There are other vendors with host based replication such as XOSoft HA which automates the entire process for one SQL server. But EMC can’t seem to come up with a solution for their own SAN products?

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