Product : DataCore, SSY [SDS]/10.0 PSP12, x86
Feature : Data Locality, General, Storage Support
Content Owner:  Herman Rutten
DataCores core approach is to provide storage resources to the applications without having to worry about data locality. But if data locality is explicitly requested, the solution can partially be designed that way by configuring the first instance of all data to be stored 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.

By default data does not automatically follow the VM when the VM is moved to another node. However, virtual disks can be relocated on the fly to other DataCore node without losing I/O access, but this relocation takes some time due to data copy operations required. This kind of relocation usually is done manually, but we allow automation of such tasks and can integrate with VM orchestration using PowerShell for example.

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.