Dynamic clusters differentiate themselves from standard VxRail clusters with the resource selected for primary storage. With standard clusters, stretched clusters and 2-node clusters, there is a dependency on the local vSAN datastore as the primary storage resource. With a dynamic cluster, none of the disk drives on the nodes are reserved to form a vSAN datastore. Therefore, an external storage resource is required to support workload and applications.
A dynamic cluster may be preferable to a standard cluster in these situations:
- The acquisition cost for VxRail nodes in a dynamic cluster is lower because they do not require local disk drives or a vSAN license.
- You already have an investment in compatible external storage resources in your data centers that can serve as primary storage for a dynamic cluster.
- The business and operational requirements for the applications targeted for the VxRail cluster can be better served with existing storage resources.
- The likelihood of stranded assets through node expansion is less likely with a dynamic cluster.
If a dynamic cluster is the best fit for your business and operational requirements, be aware of the following:
- The target data center for the VxRail cluster must support one of two options for primary storage.
- Any performance issues that are diagnosed at the storage level may be related to infrastructure outside of VxRail, and must be managed separately.
- While VxRail has deep visibility and control of a local vSAN datastore on a standard cluster, it does not have this same level of manageability with an external storage resource.
One of the two external storage resources supported with dynamic clusters is Fibre Channel storage. In this model, a compatible Fibre Channel storage array can be configured to supply a single VMFS datastore or multiple datastores to a VxRail dynamic cluster.
Figure 13. Dynamic cluster using FC-connected VMFS for primary storage
This option has the following pre-requisites:
- Verify that the storage array in your data center you have planned for support of dynamic cluster is supported with VxRail. Consult the VxRail Support Matrix to verify compatibility.
- Verify you have sufficient free capacity on the storage array. A VxRail dynamic cluster requires a minimum VMFS device of 800 GB to support workload and applications.
- At the time of ordering, include enough compatible Fibre Channel adapter cards. VxRail recommends a minimum of two Fibre Channel adapter cards per node for redundancy, although a single dual-port adapter card can be used.
- Verify that you have sufficient open ports on your Fibre Channel switches to accommodate the connections required from each VxRail node.
Another option to use for primary storage with dynamic clusters is an existing vSphere or VxRail cluster with a local vSAN datastore in your data center. The virtual machines running on the dynamic cluster will use the storage resource on the vSAN datastore, and the compute resources on the local nodes.
Figure 14. Dynamic cluster using a remote vSAN datastore for primary storage
If you choose to pursue this second option, ensure that the following guidelines are understood:
- Verify the standard cluster being targeted to supply storage resources to the dynamic cluster is at a support VxRail version. Consult the VxRail Support Matrix to verify if an upgrade is needed on this cluster.
- The standard cluster and any dynamic cluster connected to this remote vSAN datastore must be configured on the same vCenter instance under a common data center object.
- If you already have a standard cluster that is sharing its vSAN datastore to other clusters, ensure that you have not reached the maximum of five clusters already mounted to this vSAN datastore.
- The physical Ethernet network in your data center must support connectivity between the standard cluster nodes and the dynamic cluster nodes.
- If Layer 3 connectivity is required, routing settings such as static routes or BGP must be configured.
- The RTT latency between the standard cluster and dynamic cluster nodes must be less than 5 millisecond.
- Routable IP addresses must be used on the VMkernel adapters supporting vSAN on both the standard cluster nodes and dynamic cluster nodes.