Friday 13 January 2012

Hyper-V Failover Cluster: A Big Picture View Of How It Works

This post is from a post just made on the TechNet Forums: Shared LUN between VM’s.


I am new to Hyper-V and have a question about a shared LUN between two VM's. I Have a LUN on a Dell SAN and I have granted access to it to a group of servers within the Dell Storage Manager. I can mount the volume on both VM's  but when I put data on the volume on one server the other server does not see the same data. Is this by design or am I doing something wrong? Can I not mount a shared LUN on two VM's at the same time so they both see the same data?

Our Answer

What you are trying to do is like trying to connect one physical hard drive to two different servers. This is not possible.

If you are looking to make that data redundant so that if one server fails the other keeps sharing it then you need a failover cluster.

In that case two physical machines are connected to the same storage and run Hyper-V in Failover Cluster mode. On top of Hyper-V will run what is called a Highly Available Virtual Machine with Windows Server 2008 R2 SP1 as an Operating System. That Virtual Machine would be set up to connect to the shared storage and deliver the shared folders to your network.

If Node 1 in the failover cluster fails then Node 2 takes over. If the VM was running on Node 1 at the time of the failure then the VM will behave just like a physical server would if the reset button was hit. The VM will transfer to Node 2 and boot the OS back up.

If the VM was already on Node 2 then things keep humming along while the problems with Node 1 are addressed.

If Node 1 fails and the shared storage is hosted on Node 1 all of the Reads/Writes to that storage get cached by the cluster until Node 2 takes the shared storage over. Once Node 2 takes over, this can take a few seconds, all of the Reads/Writes to that shared storage get done on the actual SAN.

Windows Server 8 looks like it may have a somewhat different approach to this dilemma but we have not approached it beyond building a standard Hyper-V Failover Cluster using 2 nodes and a DAS SAN on the Developer Preview currently available as of this writing.


We believe that a Hyper-V Failover Cluster is an excellent option for clients that are downtime conscious. We have done a number of SBS 2011 deploys on a 2 node failover cluster setup with our clients being quite satisfied with the performance and enhanced availability for their critical data and e-mail.

Philip Elder
Microsoft Small Business Specialists
Co-Author: SBS 2008 Blueprint Book

*Our original iMac was stolen (previous blog post). We now have a new MacBook Pro courtesy of Vlad Mazek, owner of OWN.

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