This blog post explains how to share a VMDK between two virtual machines so they can be clustered or any application that needs two machines to share their disks.
Assume there are two VMs that participate in the clustering
Node-01 and Node-02
Create a Virtual disk on Node-01 that has to be shared with Node-02
Add a hard disk by clicking on Add a hardware and select Hard disk and click Next
Select Create a new virtual disk
Choose SCSI (1:0) which creates a fresh SCSI controller apart from the default one created during virtual machine creation and click Next
Click on Finish
Click on the newly created SCSI controller and change the SCSI Bus sharing option to “Physical”
Click on OK and power ON the machine
Now the newly added disk shows up on the Node-01 machine as /dev/sdb.
We need to add the Virtual disk created on Node-01 to Node-02
Click on Edit Setting of Node-02 machine and select Add hardware and click on hard disk
And click Next
Click on “use an existing virtual disk” and click Next
Browse to the location where Node-01’s VMDK file is present and select it
Confirm the path and click Next
Select SCSI (1:0) which creates a new SCSI controller on Node-02
Review the changes and click Finish
Select the newly created SCSI controller and select Physical under SCSI bus sharing option and click OK
Power on Node-02 and confirm that Node-01’s shared disk is showing up on Node-02
You might want to turn the Multi-writer flag in the advanced options of VM so you can let the machines write to the disk. Follow the below link for the same
Note: This might cause some problems while doing vMotion of the machines involved in clustering. So do some research before you do it.