Product : StarWind, Virtual SAN [SDS]/13279, x86
Feature : Data Locality, General, Storage Support
Content Owner:  Herman Rutten
StarWinds core approach is to keep data close (local) to the VM in order to avoid slow data transfers through the network and achieve the highest performance the setup can provide. The solution is designed to store the first instance of all data on locally available storage (primary path) and the mirrored instance to be stored on the alternate path (secondary path). Furthermore every hypervisor host can have a local preferred path, indicated by the ALUA path preference. Data does not automatically follow the VM when the VM is moved to another node.

Whether data locality is a good or a bad thing has turned into a philosophical debate. Its true that data locality can prevent a lot of network traffic between nodes, because the data is physically located at the same node where the VM resides. However, in dynamic environments where VMs move to different hosts on a frequent basis, data locality in most cases requires a lot of data to be copied between nodes in order to maintain the physical VM-data relationship. The SDS/HCI vendors today that choose not to use data locality, advocate that the additional network latency is negligible.