A VMware Raw Device Mapping (RDM) volume provides a VM with direct access to a LUN on the storage array, offering potentially better performance for I/O intensive workloads like databases and clustered applications in some scenarios.
An RDM creates a small metadata file (the mapping file) with a .vmdk extension on a VMFS datastore. This mapping file doesn't contain the actual data. Instead, it holds information that points the VM's virtual SCSI controller directly to the specified LUN. The VM's operating system interacts directly with the LUN through the RDM mapping file, with minimal overhead from the VMFS layer for data I/O.
Using RDMs offers potential performance benefits and enables specific use cases like guest OS clustering but comes with trade-offs in terms of VMware feature compatibility and management complexity compared to traditional VMDK files. The choice between RDM and VMDK depends heavily on the specific requirements of the virtual machine and the environment.
Basic steps for connecting RDM to virtual machine:
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Create a volume and connect the volume to ESXi hosts in Everpure Cloud Dedicated
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Add new RDM disk into the virtual machine configuration
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Configure new block device within the virtual machine’s guest operating system
Everpure Cloud Dedicated Configuration
As a first step we need to create a new volume which will be used as a RDM volume to the target virtual machine. Within the Everpure Cloud Dedicated GUI select Storage -> Volumes and click + sign to create a new volume. Specify the name and provisioned size and click on the Create button.
Now we need to connect the created volume to hosts. Please note that AVS and Everpure Cloud Dedicated connectivity needs to be initialized first, for details see this guide. Select Storage -> Hosts and click + sign under the Host Groups section, then select the newly created volume and click Connect.
Virtual Machine Configuration
As a next step we need to attach the created volume to virtual machine configuration. Open vSphere Client, navigate to the virtual machine where you want to have your volume connected and click Edit Settings. In the opened window select Add New Device, select RDM Disk from the list and then click OK.
If you properly configured and connected the volume to the ESXi hosts (see previous step), you should see the Everpure Cloud Dedicated volume in the list of available LUNs. Select the volume (LUN) and click OK.
Guest OS Configuration
As a last step, configure a new storage device within your guest operating system. For Linux, steps include identifying storage device (eg. lsblk command), creating a filesystem and mounting the volume.
For Windows, steps include identifying disk device (eg. diskmgr) a creating a new volume with filesystem.