I need to build a new MS cluster server on my vSphere 7 environment. I've mapped 1 RDM disk with 200GB and another with 500GB on the hosts. I created the first VM mapped with RDM without problem. But when create the second VM I want to add the same RDM disks I not able to find the same RDM Disk or the same LUNid of the RDM disk.
I test back on the vSphere 6 environment using vSphere client have no issue adding the same RDM disks on the VMs.
How are you trying to add the RDM to the second node?
Once an RDM has been added to a VM, you'll have to use the "Use existing virtual disk" option for additional VMs, and select the .vmdk descriptor file that's been created with adding the RDM to the first VM.
>>> ... where both VM are added the same RDM Disks.
Using the same descriptor/mapping file, means that both VMs use the same LUN.
Mapping the same RDM LUN using different descriptor/mapping files may cause issues.
In case you want to do this anyway - taking possible data corruption into account - see e.g. https://kb.vmware.com/s/article/1010513
enable Multi-writer is a must? Because if not enable multi-writer, I can only power up one of the node only and the other not able to power up. It will show error "File system specific implementation of Ioctl[file] failed Failed to start the virtual machine. Module 'Disk' power on failed. Cannot open the disk '/vmfs/volumes/vm file path/vmname.vmdk' or one of the snapshot disks it depends on"
Do NOT enable "Multi Writer" for an WSFC. WSFC is a "shared-nothing" cluster, where only one node at a time must access a given disk/file system. Otherwise you'd end up with file system corruption.
Please see https://docs.vmware.com/en/VMware-vSphere/7.0/vsphere-esxi-vcenter-server-70-setup-wsfc.pdf (pages 20ff) for how to add RDMs to the VMs for a CAB "Cluster-across-Boxes" configuration.