18.4. NVDIMM access modes

With devdax, NVDIMM devices support direct access programming as described in the Storage Networking Industry Association (SNIA) Non-Volatile Memory (NVM) Programming Model specification. In this mode, I/O bypasses the storage stack of the kernel. Therefore, no Device Mapper drivers can be used.

Device DAX provides raw access to NVDIMM storage by using a DAX character device node. Data on a devdax device can be made durable using CPU cache flushing and fencing instructions. Certain databases and virtual machine hypervisors might benefit from this mode. File systems cannot be created on devdax devices.

Devices in this mode are available as /dev/daxN.M. After creating the namespace, see the listed chardev value.

With fsdax, NVDIMM devices support direct access programming as described in the Storage Networking Industry Association (SNIA) Non-Volatile Memory (NVM) Programming Model specification. In this mode, I/O bypasses the storage stack of the kernel, and many Device Mapper drivers therefore cannot be used.

You can create file systems on file system DAX devices.

Devices in this mode are available as /dev/pmemN. After creating the namespace, see the listed blockdev value.

Presents a memory disk that does not support DAX. In this mode, namespaces have several limitations and should not be used.

Devices in this mode are available as /dev/pmemN. After creating the namespace, see the listed blockdev value.