Convert RDM to VMDK in VMware vSphere Virtualization using Storage vMotion Process

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Convert RDM to VMDK in VMware vSphere Virtualization using Storage vMotion Process

1. Description of RDM and How to Convert RDM (Raw Device Mapping) to VMDK in VMware vSphere Virtualization using Storage vMotion Process

   In VMware vSphere Server Virtualization Environment Architecture, Raw Device Mapping (RDM)is an option that enables LUN (Logical Unit Number) to be directly connected to a virtual machine (VM) from the storage area network (SAN), RDM (Raw Device Mapping) also has another meaning that is a protocol enhancement to USITT DMX512 that allows bi-directional communication between a lighting or system controller and attached RDM (Raw Device Mapping) compliant devices over a standard DMX line.
   
   VMDK (Virtual Machine Disk) is a file format that describes containers for virtual hard disk drives to be used in virtual machines like VMware vSphere Server Virtualization, VMware Workstation, VMware Player or VirtualBox.
   
   Storage vMotion is a component or feature of VMware vSphere Server Virtualization Environment Architecture that allows the live storage or datastore migration of a running virtual machine's (VM) file system from one storage system to another works in background, with no downtime for the virtual machine (VM) or service disruption for end users.
   
   In this article i will show you on how to Convert RDM to VMDK in VMware vSphere Server Virtualization Environment Architecture using Storage vMotion Process, then a big question is how does vmotion works in background without downtime for the virtual machine (VM) or service disruption for end users?? The question is during Storage vMotion process, VMware vSphere Server Virtualization Environment Architecture ensure that the source VM can be operated on the chosen destination Storage System.



2. Why Convert RDM to VMDK

   Although VMware recommends VMFS for the vast majority of Virtual Machine (VM), Still lots of Benefits of Raw Device Mapping (RDM), one of the most reason VMware Administrators Creating/Adding a Raw Device Mapping (RDM) to a Virtual Machine (VM) is dedicate storage to Virtual Machine (VM) and Raw Device Mapping (RDM) is recommended for those cases. Some of the commons uses of RDM are in cluster data and quorum disks for configurations using clustering between virtual machines or between physical and virtual machines or for running SAN snapshot or other layered applications in a virtual machine
   
   If you type on Google Search Engine, you will found thousands moreover millions article just with a litle keyword rdm vs vmdk on VMware vSphere Server Virtualization Environment Architecture. lets let's review Performance Characteristics of VMFS/VMDK and RDM :

   • Raw Device Mapping (RDM)

     • Raw Device Mapping (RDM) is a storage volume can't support one or many Virtual Machine (VM)
     • Raw Device Mapping (RDM) is a mapping file in a VMFS volume that acts as a proxy for a raw physical device
     • Raw Device Mapping (RDM) contains metadata used to manage and redirect disk accesses to the physical device

   • VMFS(Virtual Machine File System)/VMDK (Virtual Machine Disk)

     • VMFS(Virtual Machine File System)/VMDK (Virtual Machine Disk) is a storage volume can support one or many Virtual Machine (VM)
     • VMFS(Virtual Machine File System)/VMDK (Virtual Machine Disk) is a special high performance file system offered by VMware to store ESX Server virtual machines
       
     • VMFS(Virtual Machine File System)/VMDK (Virtual Machine Disk) is a distributed file system that allows concurrent access by multiple hosts to files on a shared VMFS volume
   From the above Performance Characteristics of VMFS/VMDK and Raw Device Mapping (RDM), I've done with my own research on my personal LAB that CPU and Memory Performance not realy have significant difference. You need to know that when you start to use RDM, two types of RDM are Physical Mode and Virtual Mode. Frequency mode used is physical, it is because a highly flexible SAN architecture lets you choose this (to detail the differences and the benefits of physical mode and virtual mode mode please find its own article), i will describe the different between them on another article.

3. How to Convert RDM to VMDK in VMware vSphere Virtualization using Storage vMotion Process

   There is three steps Convert RDM to VMDK in VMware vSphere Virtualization using Storage vMotion Process, below for step by step :
   • Convert RDM with Physical Mode Compability to RDM with Virtual Mode Compability
     The method only valid if the mode RDM you run with the virtual mode, if you've already set RDM as physical mode, then you need to turn it into a virtual mode. Changing from physical to virtual mode need a virtual machine restart (important to check the mark on the option "delete files from a datastore"). Before you begin, please write-down information about "virtual device node" where there is dropdown menu "SCSI (xxxx), when you re-connecting RDM you must fill information "virtual device node" same as Physical Mode.
   • Reconnectiong RDM with Virtual Compability Mode
     If you have done with instruction above, below capture step by step reconnecting Raw Device Mapping (RDM) with virtual mode compability
     
   • Storage vMotion
     If completed, please restart your virtual machine. Log in to the storage management of the Guest OS and make sure your RDM storage is online (if offline status, then you need to turn it into online). If all steps have been done, the final step is to change the RDM into VMDK. Run Storage vMotion, make sure you've selected RDM will run Storage vMotion and do not choose the "same format as the source". Look at below capture for detail
     

4. How do you choose RDM vs VMFS formats in VMware vSphere Virtualization

   Since Raw Device Mapping (RDM) can't support one or many Virtual Machine (VM), VMFS/VMDK is a good solution for High Availability for Storage Usage. If you run your system in VMware vSphere Server Virtualization Environment Architecture, VMFS(Virtual Machine File System)/VMDK (Virtual Machine Disk) is a special high performance file system offered by VMware to store ESX Server virtual machines.

Very easy enough, if you liked this article please share and subscribe for get update a new article. If you have any questions please leave your message through the comments form below, I will respond as soon as possible

** Note : Pay attention to every detail steps that informed, failure or damage to your system or data is not my responsibility "Do With Your Own Risk" or you can do research through the Lab to minimize your system failure

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