You can expand an existing Virtual SAN cluster by adding hosts or adding devices to existing hosts, without disrupting any ongoing operations.
Use one of the following methods to expand your Virtual SAN cluster.
Add new ESXi hosts to the cluster that are configured using the supported cache and capacity devices. See Add a Host to the Virtual SAN Cluster. When you add a new device or a add a host with capacity, Virtual SAN does not automatically distribute data to the newly added device. To enable Virtual SAN to distribute data to the devices that are recently added, you must perform manual rebalance operation in the cluster by using the Ruby vSphere Console (RVC). See Manual Rebalance.
Move existing ESXi hosts to the Virtual SAN cluster by using host profile. See Configuring Hosts Using Host Profile. New cluster members add storage and compute capacity. You must manually create a subset of disk groups from the local capacity devices on the newly added host. See Create a Disk Group on a Virtual SAN Host.
Verify that the hardware components, drivers, firmware, and storage I/O controllers that you plan on using are certified and listed in the VMware Compatibility Guide at http://www.vmware.com/resources/compatibility/search.php. When adding capacity devices, make sure that the devices are unformatted and not partitioned, so that Virtual SAN can recognize and claim the devices.
Add new capacity devices to ESXi hosts that are cluster members. You must manually add the device to the disk group on the host. See Add Devices to the Disk Group.