vmkfstools have two flag for creating raw device mapping (RDM).
-r, --createrdm /vmfs/devices/disks/... Map a raw disk to a file on a VMFS file system. Once the mapping is established, it can be used to access the raw disk like a normal VMFS virtual disk. The ´file length´ of the mapping is the same as the size of the raw disk that it points to.
-z, --createrdmpassthru /vmfs/devices/disks/... Map a passthrough raw disk to a file on a VMFS file system. This allows a virtual machine to bypass the VMKernel SCSI command filtering layer done for VMFS virtual disks. Once the mapping is established, it can be used to access the passthrough raw disk like a normal VMFS virtual disk.
One saids passthrough and the other is just raw disk.
I was wondering what's the difference between the two and which is better or more preferred on a NAS or SAN environment?
Thanks in advance