You can expand an existing vSAN cluster by adding hosts or adding devices to existing hosts, without disrupting any ongoing operations.
Use one of the following methods to expand your vSAN cluster.
Add new ESXi hosts to the cluster that are configured using the supported cache and capacity devices. See Add a Host to the vSAN Cluster. When you add a device or add a host with capacity, vSAN does not automatically distribute data to the newly added device. To enable vSAN to distribute data to recently-added devices, you must manually rebalance the cluster by using the Ruby vSphere Console (RVC). See Manual Rebalance.
Move existing ESXi hosts to the vSAN 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 vSAN 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 vSAN 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.