Configure DCPMM in VMware ESXi for AppDirect Mode

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Updated:December 21, 2020

Document ID:216546

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Introduction

This document describes the process to configure ESXi on Unified Computing System (UCS) B series servers using Intel® Optane™ Persistent Memory (PMEM) in host managed mode.

Prerequisites

Requirements

Cisco recommends that you have knowledge of these topics:

UCS B series
Intel® Optane™ Data Center Persistent Memory Module (DCPMM) concepts
VMware ESXi and vCenter Server administration

Ensure that you meet these requirements before you attempt this configuration:

Refer to the PMEM guidelines on the B200/B480 M5 specification guide.
Ensure the CPU is second generation Intel^® Xeon^® Scalable processors.
PMEM/Dynamic Random Access Memory (DRAM) ratio meets requirements as per KB 67645.

ESXi is 6.7 U2 + Express Patch 10 (ESXi670-201906002) or later. Earlier 6.7 releases are not supported.
UCS Manager and Server are in a 4.0(4) version or above. For the latest recommended version please visit www.software.cisco.com/.

Components Used

The information in this document is based on these software and hardware versions:

UCS B480 M5
UCS Manager 4.1(2b)

The information in this document was created from the devices in a specific lab environment. All of the devices used in this document started with a cleared (default) configuration. If your network is live, ensure that you understand the potential impact of any command.

Background Information

In UCS Servers configured for App Direct mode, VMware ESXi virtual machines access to Optane DCPMM Persistent memories Non-Volatile Dual In-Line Memory Modules (NVDIMMs).

Intel Optane DCPMM can be configured through the IPMCTL management utility through the Unified Extensible Firmware Interface (UEFI) shell or through the OS Utilities. This tool is designed to perform some of the next actions:

Discover and Manage Modules
Update and configure Module firmware
Monitor Health
Provision and configure Goal, Region, and Namespaces
Debug and troubleshoot PMEM

UCS can be configured using a persistent memory policy attached to the service profile for ease of use.

The open-source Non-Volatile Device Control (NDCTL) utility is used to manage the LIBNVDIMM Linux Kernel subsystem. The NDCTL utility allows a system to provision and performs configurations as regions and namespaces for OS use.

Persistent memory added to an ESXi host is detected by the host, formatted, and mounted as a local PMem datastore. In order to use the PMEM, ESXi uses the Virtual Machine Flying System (VMFS)-L file system format, and only one local PMEM datastore per host is supported.

Different from other datastores, the PMEM datastore does not support tasks as traditional datastores. The VM home directory with the vmx and vmware.log files cannot be placed on the PMEM datastore.

PMEM can be presented to a VM in two different modes: Direct-Access Mode and Virtual Disk mode.

Direct-Access Mode

VMs can be configured for this mode by presenting the PMEMregion in the form of an NVDIMM. VM Operating System must be PMem-aware to use this mode. Data stored on NVDIMM modules can persist across power cycles since the NVDIMM act as byte-addressable memory. NVDIMMs are automatically stored on the PMem datastore created by the ESXi when formating the PMEM.

Virtual Disk Mode

Intended for traditional and legacy OS residing on VM in order to support any hardware versions. VM OS is not required to be PMEM-aware. In this mode, a traditional Small Computer System Interface (SCSI) virtual disk can be created and used by the VM OS.

This document describes the configuration to use a Virtual Machine in Direct-Access mode.

Configure

This procedure describes how to configure ESXi on UCS Blade series servers using Intel Optane DCPMM.

Configure the Service Profile

1. In UCS Manager GUI, navigate to Servers > Persistent Memory Policy and click on Add as shown in the image.

2. Create Goal, ensure the Memory Mode is 0% as shown in the image.

3. Add the PMEM Policy to the desired Service Profile.

Navigate to Service Profile > Policies > Persistent Memory Policy and attach the policy created.

4. Verify the region's health.

Navigate to the selected Server > Inventory > Persistent Memory > Regions. The type AppDirect is visible. This method creates one region per CPU Socket.

Verify ESXi

1. In the Web console, the host displays the total PMEM available.

2. ESXi displays a special datastore composed of the total amount of PMEM, as shown in the image.

Configure Virtual Machine NVDIMM

1. In ESXi, virtual machines access to Optane DCPMM PMEM as NVDIMMs. In order to assign an NVMDIMM to a virtual machine, access the virtual machine through vCenter and navigate to Actions > Edit Settings, click on ADD NEW DEVICE and select NVDIMM as shown in the image.

Note: When you create a virtual machine, ensure that the OS compatibility meets the minimum required version that supports Intel® Optane™ Persistent Memory, otherwise the NVDIMM option does not appear in the selectable items.

2. Set the size of NVDIMM as shown in the image.

Configure Namespace in the Virtual Machine

1. The NDCTL utility is used to manage and configure the PMEM or NVDIMM.

In the example, Red Hat 8 is used for configuration. Microsoft has PowerShell cmdlets for persistent memory namespace management.

Download the NDCTL utility by using the available tool as per the Linux Distribution

For example:

# yum install ndctl
# zypper install ndctl
# apt-get install ndctl

2. Verify the NVDIMM region and namespace created by default by ESXi, when the NVDIMM is assigned to the virtual machine, verify space matches with configuration. Ensure the mode of the namespace is set to raw this means ESXi has created the namespace. In order to verify, use the command:

# ndctl list -RuN

3. (Optional) If the namespace has not been created already, a namespace can be created with the command:

# ndctl create-namespace

The ndctl create-namespace command creates a new namespace in fsdax mode by default and creates a new /dev/pmem([x].[y]) device. If a namespace has been created already, this step can be skipped.

4. Select the PMEM access mode, the modes available for configuration are:

Sector Mode:

Presents storage as a fast block device, this is useful for legacy applications that are still not able to use persistent memory.

Fsdax Mode:

Allows the persistent memory devices to support direct access to the NVDIMM. File system direct access requires the use of fsdax mode, in order to enable the use of the direct access programming model. This mode allows the creation of a file system on top of the NVDIMM.

Devdax Mode:

Provides raw access to persistent memory using a DAX character device. File systems cannot be created on devices using devdax mode.
Raw Mode:

This mode has several limitations and is not recommended for using Persistent Memory.

In order to change the mode to fsdax mode, use the command:

ndctl create-namespace -f -e <namespacex.y> --mode fsdax

If there is a dev already created, the dev namespace is used to format and modify the mode to fsdax.

Note: These commands require that the account has root privileges, sudo command might be required.

5. Create a directory and filesystem.

Direct Access or DAX is a mechanism that allows applications to directly access persistent media from the CPU (through loads and stores), bypassing the traditional I/O stack. DAX-enabled persistent memory file systems include ext4, XFS, and Windows NTFS.

Example of XFS file system created and mounted:

sudo mkdir < directory route (e.g./mnt/pmem) >
sudo mkfs.xfs < /dev/devicename (e.g. pmem0) >

6. Mount the file system and verify that is successful.

sudo mount <file system > < directory >
df -h < directory >

The VM is ready to use PMEM.

Troubleshoot

Is generally recommended to mount this DAX-enabled file system using the -o dax mount option, if an error is found.

Filesystem repair is executed to ensure integrity.

As a workaround, the mount can be mounted without the -o dax option.

Note: In xfsprogs version 5.1, the default is to create XFS file systems with the reflink option enabled. Previously it was disabled by default. The reflink and dax options are mutually exclusive which causes the mount to fail.

"DAX and reflink cannot be used together!" the error can be seen in dmesg when the mount command fails: