Raw device mapping
Raw Device Mapping ( RDM , English for direct device reference ) describes an option in the VMware server virtualization environment to connect a data storage device to a virtual machine .
Clarification of terms, definition
RDM is one of two ways to connect a data store to a virtual machine. The other way to connect a data store to a virtual machine is via VMFS .
While VMWare's VMFS is recommended for most applications including databases, customer relationship management, and enterprise resource planning , RDM provides a way to operate data stores in both virtual and physical environments.
Since RDM enables the use of existing SAN commands, it is generally used to improve the performance of I / O-intensive applications.
Compatibility Modes
RDM can be configured in either virtual compatibility mode or physical compatibility mode.
Virtual compatibility mode
Virtual mode offers benefits similar to VMFS such as advanced file locking and snapshots.
Physical compatibility mode
Physical mode provides access to most of the hardware functions of the storage system that is being mapped.