I recently had to connect two 4TB sata disks to a server to provide some raw storage to the network. Going on past experiences I didn’t want to virtualise the disks but rather present them to the virtual machine guest as a raw device mapping (RDM).

You will need a separate datastore that is separate to the ones you are attaching. It will have to be VMFS5 to get around the 2TB limit with VMFS3.

Note: This is not supported by VMware to the best of my knowledge.


  1. Start a SSH session to the VMware ESX host (or if on the physical server, drop to console)
  2. Run fdisk to see the disk layout.
fdisk –l
  1. You will need to find the vml identifier, you need to match that to the drive.
ls /dev/disks/ -l

In my example, the two I am interested in are:



  1. Now browse to the VMFS5 datastore you will be creating the RDM’s
cd /vmfs/volumes/datastorename
Browse to RDM location
  1. Best practise would be to create a folder for the RDM’s to sit in
mkdir RDMs
  1. Create the RDM’s by running the vmkfstools command (use the vml. location that you found in previous steps)
vmkfstools -r /vmfs/devices/disks/vml.01000000002020202020202020202020205a33303346325742535434303030 4TB_Disk1_RDM.vmdk -a lsilogic
vmkfstools -r /vmfs/devices/disks/vml.01000000002020202020202020202020205a33303351523246535434303030 4TB_Disk2_RDM.vmdk -a lsilogic
  1. Verify you have the files created
ls –lash
  1. Attach to virtual machine
VMware_Use_Exisiting_Virtual_Disk VMware Select RDM VMware_RDM_Attached VMware RDM_Physcial_LUN

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