vSphere Storage - ESXi 5.1 - Documentation - VMware

Snapshots Makes it possible to use virtual machine snapshots on a mapped volume.
Snapshots are not available when the RDM is used in physical compatibility
mode.
vMotion Lets you migrate a virtual machine with vMotion. The mapping file acts as a
proxy to allow vCenter Server to migrate the virtual machine by using the same
mechanism that exists for migrating virtual disk files.
SAN Management
Agents
N-Port ID Virtualization
(NPIV)
Figure 18-2. vMotion of a Virtual Machine Using Raw Device Mapping
Host 1
VM1
VMotion
VMFS volume
mapping file
address
resolution
mapped device
Host 2
VM2
Makes it possible to run some SAN management agents inside a virtual
machine. Similarly, any software that needs to access a device by using
hardware-specific SCSI commands can be run in a virtual machine. This kind
of software is called SCSI target-based software. When you use SAN
management agents, select a physical compatibility mode for the RDM.
Makes it possible to use the NPIV technology that allows a single Fibre Channel
HBA port to register with the Fibre Channel fabric using several worldwide
port names (WWPNs). This ability makes the HBA port appear as multiple
virtual ports, each having its own ID and virtual port name. Virtual machines
can then claim each of these virtual ports and use them for all RDM traffic.
NOTE You can use NPIV only for virtual machines with RDM disks.
VMware works with vendors of storage management software to ensure that their software functions correctly
in environments that include ESXi. Some applications of this kind are:
n SAN management software
n Storage resource management (SRM) software
n Snapshot software
n Replication software
Chapter 18 Raw Device Mapping
VMware, Inc. 181