There are two ways of exposing PMEM to a VM:
- vPMEMDisk: vSphere presents PMEM as a regular disk attached to the VM. No guest OS or application change is needed to leverage this mode. For example, legacy applications on legacy OSes can use this mode. Note that vPMEMDisk configuration is available only in vSphere and not in bare-metal OS.
- vPMEM: vSphere presents PMEM as an NVDIMM device to the VM. Most of the latest operating systems (for example, Windows Server 2016 and CentOS 7.4) support NVDIMM devices and can expose them to the applications as block or byte-addressable devices. Applications can use vPMEM as a regular storage device by going through the thin layer of the direct-access (DAX) file system or by mapping a region from the device and accessing it directly in a byte-addressable manner. This mode can be used by legacy or newer applications running on newer operating systems.
Figure 1 shows the details of the PMEM architecture in vSphere. More information about vSphere PMEM can be found at docs.vmware.com and storagehub.vmware.com.
Figure 1: vSphere PMEM architecture