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Microsoft Multi-site Cluster Users Rejoice

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It Is Now Possible To Have Automatic Failover In A 3 Node Cluster!

Microsoft recently released a patch that allows you to specify whether or not a cluster node can vote in in a majority quorum model. This is particularly useful in a multisite cluster configuration that consists of an even number of nodes.

http://support.microsoft.com/kb/2494036

Consider the following…

I have a two node cluster in a local site high availability and I wish to extend it to a 3rdlocation and add a single node for disaster recovery. Sound like a great plan as a multisite cluster is just about the most robust DR plan you can implement. However, you will not be able to take advantage of one of the best features of a multisite cluster – automatic recovery in the event of a site loss. If you were to lose your primary site the DR site only contains one cluster node (see Figure 1). This is just one vote out of three in the cluster so a majority cannot be obtained and Node3 will not come online automatically. The only way to make Node3 come online is to force the quorum online, which kind of defeats the purpose of multisite cluster by requiring human intervention for a failover to happen.

Figure 1 – In a typical 3 node multisite cluster if you lose the primary site the DR site cannot obtain majority so failover never occurs.
Figure 1 – In a typical 3 node multisite cluster if you lose the primary site the DR site cannot obtain majority so failover never occurs.

The only “safe” way to have automatic failover in a multisite cluster is to have an equal number of nodes in each site and to have a file share witness in a 3rd location with connectivity back to both the primary site and the DR site. This concept is a little difficult to grasp at first, so let me attempt to explain through illustrations.

Figure 2- With an even number of nodes in both locations and the file share witness in the primary site a loss of the primary site would not result in a failover as the Alternate Site would only have 2 out of 5 votes, not a majority.
Figure 2- With an even number of nodes in both locations and the file share witness in the primary site a loss of the primary site would not result in a failover as the Alternate Site would only have 2 out of 5 votes, not a majority.
Figure 3 – If the file share witness was moved to the Alternate Site a failure of the WAN would cause a false failover as the Alternate Site would form a majority and come online.
Figure 3 – If the file share witness was moved to the Alternate Site a failure of the WAN would cause a false failover as the Alternate Site would form a majority and come online.
Figure 4 – with the file share witness in a 3rd location failover will occur if the Primary Site is lost and false failovers are avoided in the case of connectivity failure between the Primary and Alternate Site.
Figure 4 – with the file share witness in a 3rd location failover will occur if the Primary Site is lost and false failovers are avoided in the case of connectivity failure between the Primary and Alternate Site.

As you can see, figure 4 represents the only reasonable configuration which supports automatic failover. However, this assumes that there are an equal number of nodes in each location. If you are stuck with the original 3-node configuration you are stuck as adding a file share witness does not help as you can never achieve a majority in the alternate site…until today! Microsoft release a patch that basically allows you to specify whether or not a node gets to vote or not. So what this means is you can build a 3-node cluster as illustrated in Figure 1, yet take advantage a file share witness in a 3rd location as illustrated in Figure 4. By simply telling one of the nodes in the Primary Site to note vote in the cluster you will allow the Alternate Site to form a majority with the file share witness and come online. Assuming connectivity to your 3rd location and Alternate Site is relatively reliable there really is no downside to the configuration shown in Figure 5.

Figure 5 – by disabling the vote on Node2 you can deploy a 3-node multisite cluster with a file share witness and safely support automatic failover to the DR site. The same concept can be applied to any cluster with an odd number of nodes.
Figure 5 – by disabling the vote on Node2 you can deploy a 3-node multisite cluster with a file share witness and safely support automatic failover to the DR site. The same concept can be applied to any cluster with an odd number of nodes.

While this is a great solution, you still need that 3rd location for the file share witness. If you don’t have that 3rd location you will just have to settle for a manual switchover and keep the file share witness in the primary site if you have an even number of nodes.

The PreventQuorum switch is also included as part of this hotfix which will also be of interest to people deploying multisite clusters. Well explore that option in a future article.

Get the hot fix here…

A hotfix is available to let you configure a cluster node that does not have quorum votes in Windows Server 2008 and in Windows Server 2008 R2

http://support.microsoft.com/kb/2494036

Reproduced with permission from https://clusteringformeremortals.com/2011/04/29/microsoft-multisite-cluster18-users-rejoice-it-is-now-possible-to-have-automatic-failover-in-a-3-node-cluster19/

SQL Server Denali And Hadron

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Microsoft’s latest version of SQL, code named Denali, is currently in CTP. One of the most anticipated feature is something called HADRON. Basically, it is has been described as mirroring 2.0. The best features of HADRON as I can see compared to mirroring as it is in 2005/2008 are as follows:

  • You can query the mirror (now known as a replica)
  • You can have more than one replica
  • Database are grouped into availability groups to ensure related databases always fail over together
  • Support for replicating more than 10 databases

If you want a great preview, check out fellow MVP Brent Ozar’s post, SQL Server Denali Rocks!

From reading Brent’s post I gather Microsoft only plans to include this in the Enterprise version of SQL. That is too bad for the many customers running SQL Server Standard as traditionally there is a significant price jump to go from Standard to Enterprise. However, that is good news for the 3rd party replication vendors out there who are providing similar functionality today on SQL 2005/2008 on Standard and Enterprise Editions.

SteelEye DataKeeper Cluster Edition for SQL Server

While it is not an exact duplicate of HADRON, a multi-site cluster using SteelEye DataKeeper Cluster Edition for SQL Server gives you a great solution for HA/DR without requiring shared storage. So while we wait for Denali and all the application vendors to start supporting Denali you might want to have a look at what SteelEye DataKeeper Cluster Edition can do for you today!

Reproduced with permission from https://clusteringformeremortals.com/2010/12/10/sql-server-denali-and-hadron/

Advanced Availability And Disaster Recovery For Hyper-V At Techdays Germany

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I recently returned from a 10 day trip to Germany where I attended CeBIT and also presented at TechDays in Hannover and Essen with Microsoft Technical Evangelists Michael Korp and Ralf Schnell . The trip was very productive and the sessions were very well attended.

Advanced Availability for Hyper-V

My portion of the session focused on Advanced Availability for Hyper-V, specifically multi-site clusters, data replication and automated disaster recovery. Have a look at the video here.

Reproduced with permission from https://clusteringformeremortals.com/2010/03/17/advanced-availability-and-disaster-recovery-for-hyper-v-at-techdays-germany/

 

Is Vmware’s Vsphere Disaster Recovery Options Really The Better One?

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Are Vmware’s Vsphere Disaster Recovery Options Really Better Than Microsoft’s Options For Hyper-V?

Every article I read about virtualization and disaster recovery says VMware has a more robust DR solution than Microsoft. Well, I’d like to challenge that assumption. From the view where I sit, this is actually one of the areas where Microsoft has a major competitive advantage at the moment. Here is how I see it.

VMware Site Recovery Manager

This is an optional additional add on that rides on the back of Array based replication solutions. The recovery point objective is good due to the array based replication. The RTO is measured in hours, not minutes. Add in the fact that moving back to the primary data center is a very manual procedure. It basically requires that you re-create your jobs in the opposite direction. The complete end to end recovery operation of failover and failback could take the better part of a day or longer.

Microsoft Multi-Site Cluster

Virtual machine HA clustering is included with the free version of Hyper-V Server 2008 R2, as well as with Windows Server 2008 Enterprise and Datacenter editions. In order to do multi-site clusters, it requires array based replication or host based replication solutions that integrate with Windows Server Failover Clustering. With a multi-site cluster, failover is measured in minutes (just about the time it takes to start a VM) and can be used with array based replication solutions such as EMC SRDF CE or HP MSA CLX or the much less expensive host based replication solutions such as SteelEye DataKeeper Cluster Edition.

Not only is failover quick with Hyper-V multi-site clusters, measured in just a few minutes. Failback is also quick and seamless as well. Add in support for Live Migrations or Quick Migration across Data Centers. I think this is one area that Microsoft actually has a much more robust solution than VMware Vsphere Disaster Recovery Options. Maybe it does not included automated DR tests, but when you consider you can failover and failback all in under 10 minutes, maybe an actual DR test performed monthly would give you a much better indication of what to expect in an actual disaster?

If you want a Hyper-V solution more like SRM, then there is an option there as well. It is called Citrix Essential for Hyper-V. But much like SRM, it is an optional add-on feature. It really doesn’t even match the RPO and RTO features that you can achieve with basic multi-site clusters for Hyper-V.

What do you think? Am I wrong or is there something I just don’t get? From my view, Hyper-V is heads and shoulders above Vsphere Disaster Recovery Options. 

Reproduced with permission by https://clusteringformeremortals.com/2010/03/10/are-vmware%E2%80%99s-vsphere-disaster-recovery-options-really-better-than-microsoft%E2%80%99s-options-for-hyper-v/

Microsoft End-To-End Cross-Site Disaster Recovery Solution

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Cross-Site Disaster Recovery Solution

Microsoft has recently updated their Virtualization Continuity page with some good information.

Implementing a reliable, rapid-recovery strategy can be time-consuming to implement and expensive to manage. Due to the complexity and cost, many companies simply don’t have comprehensive business continuity plans to protect their data and ensure application availability.

Virtualization has been a game changer for many companies. With virtualization based Site Recovery solutions, you can ensure higher availability and business continuity options. Windows Server provides support for a wide range of industry leading, shared storage solutions to deliver Quick and Live Migration. Combined with partner cross-site data management and replication technologies, Microsoft is offering complete Cross-Site Disaster Recovery Solution

In summary, Microsoft Site Recovery solutions provide these key benefits:

  • Bullet proof application and data availability across a range of applications
  • Site-wide disaster recovery that can help you gain immediate and long-term operational and capital benefits
  • Automated fail-over and fail back based on clustering and data resynchronization delivering superior application and data availability, for planned and unplanned downtime

Also, they have recently published a white paper entitled “Microsoft End-to-End Cross-Site Disaster Recovery Solutions“. This is a must read for anyone deploying SteelEye DataKeeper in a Cross-Site Disaster Recovery configuration.

Reproduced with permission from https://clusteringformeremortals.com/2009/12/22/microsoft-end-to-end-cross-site-disaster-recovery-solution/