Dynamic Disks with Windows Server Failover Clustering
Published Mar 15 2019 01:57 PM 7,737 Views

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 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 Veritas called InfoScale Storage to enable support of Dynamic Disks on Windows Server Failover Clusters. 

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 address some common misconceptions.

Large Partitions
Basic disks that use MBR partition table are limited to 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
Partitions on Basic disks support both grow and shrink on Failover Clusters with no downtime.  With a simple right-click option in the Disk Management (DiskMgmt.msc) snap-in to “Extend Volume” or “Shrink Volume”. 

Software RAID
Traditional shared storage 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.

Some customers use low cost commodity JBOD's and then want to use software RAID to create resilient shared storage.  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's not the right solution 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 Veritas InfoScale Storage.  As mentioned, using Dynamic Disks do provide a great add-on product that extends the functionality of Failover Clustering.

Microsoft's 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

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