Dynamic Disks with Windows Server Failover Clustering

Since Failover Clustering traditionally requires shared storage (you could also use hardware or software replication between nodes), we get a lot of questions about which shared storage types we support.  Windows Server Failover Clustering has a very flexible storage model that allows a wide variety of storage and volume management solutions from 3rd parties to integrate and extend the functionality of clustering.  One common question I commonly get asked is around Dynamic Disk support on Windows Server Failover Clusters, so I thought I would take a moment to address this.

Are Dynamic Disks supported on Failover Clusters?

Yes Dynamic Disks are absolutely supported on Failover Clusters, however support is not provided natively in-box in Windows Server for Failover Clusters.  It requires an add-on product from Symantec called Storage Foundation for Windows Server to enable support of Dynamic Disks on Windows Server Failover Clusters.  You can learn more about the Storage Foundation for Windows product here:

This KB article also discusses support for Dynamic Disks on Windows Server Failover Clusters: http://support.microsoft.com/kb/237853


Dynamic Disks do provide a number of different features, in this section I’ll discuss some of the frequently asked questions and dress some common misconceptions.

Large Partitions

While Basic disks that use MBR partition table only support a maximum of 2 TB partitions, basic disks that use GUID partition table (GPT) disks enable partitions that are greater than 2 TB and are fully supported in-box on Failover Clusters.

Dynamically Growing Partitions

With a simple right-click option in the Disk Management (DiskMgmt.msc) snap-in to “Extend Volume” or “Shrink Volume”.  This can be done on clustered in-box basic disks with no downtime.

Software RAID

Traditionally Failover Clusters are deployed using external storage (Fibre Channel, iSCSI, FCoE, or SAS), and all clusterable SAN class storage supports Hardware RAID.  So most customers choose to go with the Hardware RAID they already have in the storage array for disk resiliency instead of using Software RAID.

Some customers use low cost commodity JBOD’s and then want to use software RAID to create resilient shared storage.  With Windows Server 2012 this can be accomplished using the in-box Storage Spaces feature.  Spaces creates resilient storage with software from external shared JBOD’s, and is fully supported on a Failover Cluster.

Spanning Volumes

With spanning volumes, that really is a matter of how you do your SAN management when increasing capacity.  Most storage arrays these days support dynamically expanding the size of a LUN.  As I said earlier, with Basic disks you can dynamically increase the size of that volume to match the new larger LUNs.  You can also use Thin Provisioning to create LUN’s, but not fully allocate the disk space at provisioning time.  However some people prefer to concatenate LUNs and span a single volume over multiple LUNs, then they just create a new LUN and span the volume over that new LUN when they want to add capacity.  For old-school IT departments that are highly silo’d, I sometimes hear this is ‘easier’ for SAN admins to just create a new LUN, opposed to tracking down the right LUN and expanding it.  I have no right or wrong answer for you here, it’s a matter of how you manage your SAN’s.  With Storage Spaces you can use a Simple Space to combine multiple physical disks into a single logical volume, however Spaces is designed to be a SAN alternative… not another layer to put on top of your SAN.  So it doesn’t fit the bill for what most people are looking for in this specific scenario.

I hope this helps in understanding that Dynamic Disks are supported with Windows Server Failover Clustering with the add-on product from Symantec Storage Foundations for Windows.  As mentioned, using Dynamic Disks do provide a great add-on product that extends the functionality of Failover Clustering.

Microsoft’s forward looking strategy for in-box Software-defined Storage capabilities is focused on the Storage Spaces and Storage Spaces Direct features.

Elden Christensen
Principal PM Manager
Clustering & High-Availability