Creating a RDM Disk

Hi,

Creating RDM quick recap and steps to configure RDM disk. Hope its help.

What is RDM? : Raw Disk Mapping (RDM) configured through bypassing Hypervisior, RDM can talk directly SAN device (Storage). Once you configured RDM first time its create mapping file in VMFS Datastore where .VMX file reside on same DataStore and RDM has metadata for managing, configuring and control on disk access to the SAN.
RDM has two compatibility type:

1. Physical compatibility RDM (pRDM).

2. Virtual compatibility RDM (vRDM).

1. Physical RDM (pRDM) : Guest OS can send SCSI commands to SAN device without involving Hypervisior and pRDM has limition VM’s Snapshots although SAN (LUN) level sanpshost can be used as alternative solution also FT  will not work for pRDM. SIOC and vCloud Directior does not support RDM (Any compatibility)
pRDM good for Cluster use case between Physical to Virtual Cluster Node and Cluster VM (Node) distribute running on different ESXi Host (Across the box)

2. Virtual RDM (vRDM) : Here Hypervisior responsible for SCSI commands and Snapshot of VM can be taken. SIOC and vCloud Directior does not support RDM (Any compatibility) and FT will not work for vRDM.
vRDM can use Across the cluster and cluster in box, if your all cluster VM (Node) running on same.
RDM Prerequisite: A raw LUN [ max 62TB (vRDM) & 64TB (pRDM)]
RDM Creation :
Step-1 : Unused LUN with identical naa.id to choose correct one.
Step-2 : Re-Scan for new device for all HBA prior to attaching VM.
Step-3 : Select Correct VM which you want to add RDM.
Step-4 : Click on Edit setting and choose new device from bottom and select RDM Disk.
Step-5 : Select RDM Compatibility mode choosing drop down option.
Step-6 : VM should be shut down or power-off before sharing RDM disk.
Step-7 : Select Multi writer flag for shared RDM disk.
Step-8 : Shared RDM should be configured iSCSI Controller SCSI 1, 2 and 3 because SCSI 0  used for Local disk only.
Step-9 : Check with application owner if they require DISK UUID, So enable it using VM advanced option and add config parameter [disk.enableUUID=true].

Step-10 : Power on all VM that should be power on without any error.

Feel free share your suggestion for me and comment below if any thing I missed or you want to highlights.

Thanks

Kuver P Singh

A Thinker | Practitioner | Photographer

 

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