Listing currently configured diagnostic coredump partition on disk

1. Open a console session to the ESXi host, or the location where vSphere Command-Line Interface (vCLI) is installed.
2. Retrieve the currently active diagnostic partition by running esxcli command line utility:
   
   esxcli system coredump partition get
   
   You see output similar to:
   
   Active: mpx.vmhba2:C0:T0:L0:7
Configured: mpx.vmhba2:C0:T0:L0:7

Creating and activating a diagnostic coredump partition on disk

To create a new diagnostic coredump partition on disk:

1. Open a console session to the ESXi host. For more information, see the Log In to the ESXi Shell section in the vSphere Security guide.
   
   Note: Diagnostic partitions cannot be created using the vCLI, but existing diagnostic partitions can be activated.
    
2. Select a storage device with at least 100 MB of free space that is accessible by the ESXi host. For more information, see Identifying disks when working with VMware ESX/ESXi (1014953).
   
   Note:
   • Ensure the storage device you intend to use does not contain any useful data as it will be overwritten.
   • If using a non-boot local USB storage device, see Configuring a vSphere ESXi host to use a local USB device for VMkernel coredumps (1038228).
   • Any attempt to configure a remote device using the ESXi host software iSCSI initiator results with this error: Unsupported disk type: Software iSCSI LUNs are not supported.
      
3. Run the partedUtil command line utility to create a new partition, 100 MB in size, with type 0xFC = 252. Ensure that other existing partitions on the same disk are not affected. For more information, see Using the partedUtil command line utility on ESXi and ESX (1036609).
   
   Note: Some environments may require a larger size. If needed you will be prompted with the recommended size.
    
4. Run the esxcli command line utility to list all accessible diagnostic partitions. Validate that the list of partitions includes the one created in step 3.
   
   esxcli system coredump partition list
   
   You see output similar to:
   
   Name Path Active Configured
--------------------- ------------------ ------ ----------
mpx.vmhba2:C0:T0:L0:7 /vmfs/devices/.... false false
    
5. Set and activate one of the accessible diagnostic partitions using the esxcli command line utility. Either specify a device explicitly, or use the Smart Activate feature to automatically select one of the accessible diagnostic partitions:
    
   • To configure and activate a specific device partition by its VMkernel device path, run these commands:
     
     esxcli system coredump partition set --partition="Partition_Name"
esxcli system coredump partition set --enable true
     
     For example:
     
     esxcli system coredump partition set --partition="mpx.vmhba2:C0:T0:L0:7"
esxcli system coredump partition set --enable true
      
   • To automatically select and activate an accessible diagnostic partition, run this command:
     
     esxcli system coredump partition set --enable true --smart
      
6. Validate that the diagnostic partition is now active by running this command:
   
   esxcli system coredump partition list
   
   You see output similar to:
   
   Name Path Active Configured
--------------------- ------------------ ------ ----------
mpx.vmhba2:C0:T0:L0:7 /vmfs/devices/.... true true

Activating or deactivating an existing diagnostic coredump partition on disk using Host Profiles

1. Connect to vCenter Server using the vSphere Client.
2. Click Home and select Host Profiles.
3. Create or edit a host profile.
4. Select Coredump Partition Settings > Fixed Coredump Partition Policy.
5. The configuration option Enable or disable coredump partition is available. Specify the preferred option:
    
   • When deselected, the ESXi host deactivates any previously active diagnostic partition.
   • When selected, the ESXi host automatically selects and activates an accessible diagnostic partition. If a diagnostic partition is already configured, it is activated.
      
6. Save and apply the host profile.

The environment that does not have Core Dump Configured will receive an Alarm as "Configuration Issues :-  No Coredump Target has been Configured Host Core Dumps Cannot be Saved Error".
In the scenarios where the Core Dump partition is not configured and is not needed in the specific environment, you can suppress the Informational Alarm message, following the below steps,

1. Select the ESXi Host > 
2. Click Configuration > Advanced Settings
3. Search for UserVars.SuppressCoredumpWarning
4. Then locate the string and and enter 1 as the value 

To extract contents from the VMKcore diagnostic partition after a purple screen error, see Collecting diagnostic information from an ESX or ESXi host that experiences a purple diagnostic screen (1004128).

Configuring an ESXi/ESX host to capture a VMkernel coredump from a purple diagnostic screen
Identifying disks when working with VMware ESXi/ESX
Using the partedUtil command line utility on ESXi and ESX
Configuring a vSphere ESXi host to use a local USB device for VMkernel coredumps
Configuring an ESX/ESXi 3.0-4.1 host to capture a VMkernel coredump from a purple diagnostic screen to a diagnostic partition
ESXi 5.x/6.x ホスト上での診断コアダンプ用パーティションの構成
在 ESXi 5.x/6.0 主机上配置诊断核心转储分区
ESXi ホストの [サマリ] タブで次のエラーが表示される： 「vmkcore ディスク パーティションが存在しません」