What are Raw Disk Mappings?
In VMware you can create a Raw Disk Mapping to assign a physical hard drive directly to a virtual machine. This bypasses a VMFS datastore and allows you to dedicate a whole drive to a VM. One use for this would be to create a software RAID on a VM for a ESXi host that doesn’t have a supported RAID controller. Or if you are converting a physical machine to a virtual one and want to access the data without running VMware Converter.
How to create a RDM
- Ensure you don’t have a datastore on the drive you want to create a RDM.
- Get the Identifier of the drive from vSphere web client or the vSphere client
- Enable the ESXi shell by following these directions if you haven’t already done so.
- Open the ESXi shell.
- Determine the VML identifier for the disk by finding the matching VML. The VML ID will be used in the command to create the RDM.
# ls /dev/disks/ -l total 5860592008 -rw------- 1 root root 500107862016 Sep 11 23:42 t10.ATA_____ST3500630AS_________________________________________9QG6WSE4 lrwxrwxrwx 1 root root 72 Sep 11 23:42 vml.01000000002020202020202020202020203951473657534534535433353030 -> t10.ATA_____ST3500630AS_________________________________________9QG6WSE4
- Change the working directory to an existing datastore.
# cd /vmfs/volumes/datastore/
- Create the RDM
Virtual RDM: (Able to create snapshots)
# vmkfstools -r /vmfs/devices/disks/vml.01000000002020202020202020202020203951473657534534535433353030 RDM.vmdk -a lsilogic
Physical RDM: (Nearly all SCSI commands are passed directly to the disk rather being handled by the VMkernel)
# vmkfstools -z /vmfs/devices/disks/vml.01000000002020202020202020202020203951473657534534535433353030 RDM.vmdk -a lsilogic
- Add the created RDM.vmdk file to a virtual machine and enjoy.