Raw device mapping (RDM) is a mapping file that provides direct access to a LUN on an iscsi or fibre channel storage system for a virtual machine. RDM is basically a Mapping file acts as a proxy for a raw physical storage device placed in a VMFS volume. Virtual Machine can directly access the storage device using RDM and RDM contains metadata which controls the disk access to the physical device. Raw Device Mapping (RDM) gives you some of the advantages of direct access to a physical device while keeping some advantages of a virtual disk in VMFS. As a result, it merges VMFS manageability with raw device access. In this article, We are going to discuss the overview of Raw Device Mapping and difference between RDM virtual and Physical compatibility mode
Few Use cases for Raw Device Mapping
- For Microsoft cluster configuration in Virtual machine (Virtual-to-virtual (Cluster-in-a-box and cluster-across-boxes) or physical-to-virtual)
- For running SAN management software (Storage resource management software, storage array snapshot software, replication software, etc) inside a virtual machine
- For any application running on a virtual machine that needs to access a device using hardware-specific SCSI commands
- RDM is useful in physical-to-virtual conversion operations by avoiding migration of a large data LUN to a VMDK.
Types of Raw Device Mapping(RDM) Compatibility Mode
There are 2 types of Raw Device Mapping(RDM) Compatibility Mode
1.Virtual compatibility mode allows an RDM to act exactly like a virtual disk file, including the use of snapshots.
2.Physical compatibility mode allows direct access of the SCSI device for those applications that need lower level control.
11 Differences between RDM Virtual and Physical Compatibility Mode
Difference between RDM virtual and physical compatibility mode was one of the common questions people asked when we discuss RDM. Below table provides some of the important 11 differences between RDM virtual and physical compatibility mode.
I hope this article helps you to understand the some of the key difference between virtual and physical compatibility RDM disks. Thanks for Reading!!!. Be social and share it on social media, if you feel worth sharing it.