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Chapter 3: Configuring DCPMM Settings Using Open Source Utilities
Some Important Concepts for Persistent Memory Provisioning
Region
A region is a group of one or more DCPMMs. A DCPMM region can be created in either
a non-interleaved or n-way interleaved format. In a interleaved region, all DCPMMs are
seen as one single monolithic space, which is similar in concept to RAID-0 in storage. In
a non-interleaved region, each DCPMM is seen as a separate space, which is similar in
concept to JBOD in storage.
DCPMM Region
DCPMM regions can only be created or modified by using ipmctl. DCPMMs support the
following three types of regions:
•
PMEM: Persistent memory devices allow for byte-addressable access.
•
BLK: Block devices allow sector atomicity similar to traditional storage devices.
•
NVDIMM: NVDIMM modules simultaneously support PMEM and BLK mode access.
Namespace
Namespace defines a contiguously addressed range of non-volatile memory, which is
similar in concept to a hard disk partition, SCSI Logical Unit (LUN), or an NVM Express
namespace. It is a persistent memory storage unit that cannot be used for input/output.
Namespaces will appear as a device in
ndctl
(
/dev
). Creating namespaces can be achieved
by using
ndctl
(Non-volatile Device Control) in a Linux system.
DCPMM Namespace
DCPMMs can appear as one of the two types of namespaces depending on the operating
system and UEFI BIOS settings.
•
Direct Access (DAX)
DAX, which functions as a byte-addressable storage, requires an API (Application
programming interface) to access. In order to utilize the DCPMM features, applications
must be DCPMM-aware and use the published APIs.
•
Block Storage:
Block Storage is persistent memory that is seen as a block storage device by applications.
In order to utilize the DCPMM features, the operating system needs to be DCPMM-aware.
