Using Raw Device Mapping (RDM) with SAS attached storage

The ESX-Server does not “know” that the attached SAS-Storage is a shared storage (like HP MSA 2xxx) so it will not allow us to create a RDM disk file within a VM. To do this we need the CLI.

Assuming the volume is already mapped to the ESX-host and can be seen by the ESX-Host we need to do the following:

  1. Connect to the host using a SSH session
  2. Display the paths using “esxcfg-mpath -m” and look for the volume – if we know the LUN we can do a grep (e.g. “esxcfg-mpath -m |grep -i l10”  – this would only display the volume with the LUN-ID 10)
  3. Copy the naa-ID (naa.12345lotofnumbers7890)
  4. To create a RDM enter: “vmkfstools -z /vmfs/devices/disks/<your naa-id here> /vmfs/volumes/<your vmfs-volume here>/<your vm-name here>/<diskname here>.vmdk”
  5. Please note that the parameter “-z” creates a physical RDM – if you want to use a virtual RDM use the parameter “-r”
  6. Go to your VM and add a Disk
  7. Select “Existing disk” and browse to the diskfile you created in step 4
  8. Finish and do a rescan of disks in your VM
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