The total capacity of a VSA cluster is the sum of the capacities of all VSA datastores. Depending on the RAID configuration of your VSA cluster, you use different algorithms to calculate VSA capacity.

RAID Configuration and Settings

Choose from the supported configurations per the RAID Settings and Requirements. Refer to the Release Notes for supported disk and RAID combinations.

Based on RAID rules, the results yield a VMFS datastore of a certain size.

For example, if you have 6 disks of 600GB each, your yield will be as shown. Due to some overhead, all of the sizes are approximate.

  • RAID 5 yields 3TB

  • RAID 6 yields 2.4TB

  • RAID 10 yields 1.8TB

Calculating the Maximum Cluster Space Available

After the hosts are configured, an Individual Host Baseline Figure is calculated for each host.

The Individual Host Baseline Figure is calculated as Free Space that includes 23GB for system and VSA Appliance use.

The Lowest Individual Host Baseline Figure of the hosts included in the VSA cluster is used to calculate the Maximum Cluster Space Available for allocation to the cluster. The following formula is used for calculations:

(Lowest Individual Host Baseline Figure x Number of cluster members) / 2 = Maximum Cluster Space Available

Note:

The Cluster Creation wizard lets you use less of this Maximum Cluster Space Available, if you need to.

The value that you select to allocate to the cluster when you run the Cluster Creation wizard appears in the VSA Manager page after the cluster is created. The value is displayed as the Storage Capacity of the cluster.

The resulting NFS datastores and their sizes are shown as following:

  • The number of NFS datastores created and exported to each host equals the number of VSA cluster members.

  • The size of each NFS datastore is (Storage Capacity of the cluster) / (Number of cluster members) .

Example 1

In this example, use a 2-member cluster with the following configuration:

  • One host with VMFS datastore of 405G, with existing 1G virtual machine pre-allocated on local storage.

  • One host with VMFS datastore of 405G, with existing 2G virtual machine pre-allocated on local storage.

The resulting capacity is calculated as the Lowest Individual Host Baseline Figure = 403G - 23G = 380G. The Maximum Cluster Space Available = 380G x 2 / 2 = 380G.

If all of the Maximum Cluster Space Available is allocated to the cluster, its Storage Capacity would be 380G.

Example 2

In this example, use a 3-member cluster with the following configuration:

  • One host with VMFS datastore of 405G, with existing 1G virtual machine pre-allocated on local storage.

  • One host with VMFS datastore of 405G, with existing 2G virtual machine pre-allocated on local storage.

  • One host with VMFS datastore of 405G, with existing 3G virtual machine pre-allocated on local storage.

The resulting capacity is calculated as the Lowest Individual Host Baseline Figure = 402G - 23G = 379G. The Maximum Cluster Space Available = 380G x 3 / 2 = 568.5G.

If all of the Maximum Cluster Space Available is allocated to the cluster, its Storage Capacity would be 568.5G.