Vmware virtual machines comprise a set of files in typically one of two given formats. Attach newly created vmdks to vm, ideally choosing a device node of anything other than 0. Distributed locking on a raw device mapping makes it safe to use a shared raw lun without losing data when two virtual machines on different servers access the same lun. One of the drives on the server is a raw mapped lun. Take a look at the 11 differences between rdm physical vs virtual. The setup is similar to that of a virtual machine cluster that accesses the same virtual disk file, but an rdm replaces the virtual disk file.
It is not possible to storagevmotion the iscsi disks without doing some work first see below as the hypervisor does not see continue reading converting iscsi targets in. In short it means actually data is written on the disk. The question often comes up, when should i use raw device mappings rdms instead of traditional vmfs vmdk virtual disks. In this article, we will find an easy solution to map the virtual machine disks to. A vmware virtual hard disk can be made up one or multiple vmdk files. Currently a netapp filer but plans are to go nimble storage with full ssd. To enable your vms to talk directly to lun, you need a raw device mapping file. Rather than creating a virtual disk vmdk on a lun, which is generally shared with other vms and virtual disks. It makes it interesting later on down the road if youre attempting the luntovmdk conversion and ill address how to get around that later in this article. An rdm is a mapping file in a separate vmfs volume that acts as a proxy for a raw physical storage device. To import a virtual disk into a raw lun for use with an rdm in esxiesx 4. Is it better to present the pool of drives as a iscsi target to a windows fileserver directly and store files that way or connect it to a exsi server and store the data within vmdk disks.
In practice, this means that a virtual machines rdm disk maps directly to a chunk of storage, a lun. Both formats enable you to access the virtual machines disk, but they differ in approach to storage, and vmware recommends vmfs for the vast majority of vms. Raw device any scsi device accessed via a mapping file. You navigate to the vm to find the rdm in question but are faced with this so which disk needs to be expanded. Easily convert netapp luns to vhdx or vmdk files its. When a vm is configured to use a rdm, the selected lun is dedicated.
Vmdk file is the virtual disk image file created by vmware software. Mark achtemichuk over at vmware published a great article the other day on the use of vmdks virtual machine disk versus rdms in vmware vsphere 5. The reasons for doing this should purley be for functional and management reasons, not performance. Traditionally, a vm disk or vmdk consists of storage space carved out of the underlying. So if you dont delete the vmdk from the disk you wouldnt find the raw lun when you attempt to reattach it much later. Currently a netapp filer but plans are to go nimble. This tip defines virtual disks, explains the three main types of virtual disks and makes recommendations on when to use each type. The rdm allows a virtual machine to directly access and use the storage device and before proceeding with the move, the virtual machine where the rdm is currently attached must be shut down. It can be confusing when trying to identify the rdm that correlates to a windows drive. All the files have been removed from this drive and it is no longer needed for the server. Provides somewhat less vsphere storage tooling than vmdk. The mapped device appears to the guest operating system exactly the same as a virtual disk file in a vmfs volume.
If you are moving sql server or oracle data from rdm to vmdk, please use the advanced tab in the migration wizard to specify thick provisioned. As a result, it merges vmfs manageability with raw device access. If you are using a raw disk in virtual mode, you can realize the benefits of vmfs such as advanced file locking for data protection and snapshots for streamlining development processes. Rdms can be presented in either virtual compatibility mode or rdmv or physical compatibility mode or rdmp.
This is also the first time weve mapped a raw lun to esxi like this and wt veeam backup, hence why i thought they were related along with veeam seeing the vm as having 50gb total size, and 30gb processed size. Virtual compatibility mode allows a mapping to act exactly like a virtual disk file. Vmware virtualization rdm to vmdk migration house of. Now if your doing this for anything else, i do have a patented double lun swapparo system to do this with less than 5 minutes of downtime, and no robocopyfile copy. Converting rdms to vmfs envision technology advisors blog. Mapping file a vmfs file containing metadata used to map and manage a raw device. Our infrastructure is setup in a very traditional manor ie all the san storage is presented to the vms as luns using the iscsi initiator within the vms. Cleaning up the mapped rdm luns in the guest operating system and esx server. The answer for this usually is, always use vmfs unless you fit into specific use cases.
There are two compatibility modes for raw device mappings, virtual and physical. Convert iscsi mapped disk to vmware vmdk solutions. Raw mapped lun vs vmdk files williambishop dec 4, 2008 5. Powercli script to identify which vm is using an rdm lun. When you map a lun to a vmfs volume, vcenter server creates a raw device mapping rdm file that points to the raw lun. Recently i was tasked with converting iscsi connected disks on windows servers to a new san. An rdm is raw lun that is presented directly to a vm instead of creating a traditional virtual disk on a vmfs datastore. Mapping file a vmfs file containing metadata used to map and manage a.
To open vmdk file, please follow the steps, click the open button on toolbar or choose file open menu to open vmdk file. When creating the rdm pointer file, should we be using virtual or physical compatibility mode in vmware. Once storage vmotion is completed, virtual rdm disk will be converted to vmdk. If you want to do faster p2vs you can just convert the c. As it turned out, this was a pretty easy task as we were on vsphere 5 and i had some free storage on the san to deploy a new lun for the server. Find out how in this guide to the basics of vm storage. Convert raw mapped lun from a virtual to physical or vice versa. Finally, we have the vmdk file based disk, which is a fully virtualized storage device. The question often comes up, when should i use raw device mappings rdms instead of traditional vmfsvmdk virtual disks. With this migration it was decided that we should convert the disks to native esxi vmdk format. Just make sure you attach them to a scsi controller of the same type above. It rdm not raw lun is referred in the virtual machine configuration. The vmware team has published a lot of evidence in the past that the difference is very minor, in fact difficult to measure accurately and probably unperceivable to.
A raw disk mapping rdm can be used to present a lun directly to a virtual machine from a san. Take a look at the 11 differences between rdm physical vs virtual compatibility mode. Please note, you cannot convert a lun to a target vhd directly on the volume figure 3 the target vhd has to be within a lun. Vmware rdm raw device mapping is a mapping file that provides direct access to a lun on an iscsi or fibre channel storage system for a virtual machine. Aug 25, 20 if you want to do faster p2vs you can just convert the c. Raw device mapping makes it possible to use vmfs distributed locking for raw scsi devices. We have explained the detailed 11 differences between rdm physical vs. Now if your doing this for anything else, i do have a patented doublelun swapparo system to do this with less than 5 minutes of downtime, and no robocopyfile copy. Each drive is a file on a file system nfs or vmfs that is presented to a vm to look like a standalone scsi volume.
Feb 19, 2007 it rdm not raw lun is referred in the virtual machine configuration. File permissions raw device mapping makes file permissions possible. Raw device mapping rdm is one way to pass a raw disk device directly through from the disk controller to the softnas cloud vm in vmware. Apr 26, 20 the original mapped lun is left alone after the migration completes, and can be removed as necessary to reclaim space. There are two types of rdm disks virtual compatibility rdm and physical compatibility rdm. Write down the drive letter of the disk in the guest os. Use an rdm with virtual machine clusters that require access to the same raw lun for failover scenarios.
How to convert rdm to vmdk the ultimate guide vmware arena. Add an rdm disk to a virtual machine in the vsphere client. Also note, that the vmdk cannot have any vmdk snapshot disks associated with it. Converting iscsi targets in windows to vmdk mikails blog. The results of this will produce a vm with vmdk disks on vmfs. Cleaning up the mapped rdm luns in the guest operating. Moving an existing rdm from one virtual machine to another some steps are required to avoid data loss and to keep the disk configuration. Vmware raw device mappingrdm lets design, implement. Jul 03, 2014 vmdk maximizes vsphere storage tooling. Doing some quick searching in the vmware kb, i found vmware articles 1005937 had a powercli script which showed the size of the rdm and the full path of the rdm. Vmware vsphere physical and virtual rdm bretts it blog.
Large vmdk vs iscsi attached san storage just wondering if anyone has any input on choosing to have a 56 tb. Colloquially, this is what is often referred to as a virtual disk vmdk. Theres no supported topology that allows you to convert a source vmdk hosted on a vmfs formatted lun. Vmware raw device mappingrdm lets design, implement and. If your san management software integrates with vsphere to auto mount the lun as a datastore, skip that step. There is a misunderstanding that rdms offer greater performance. Distributed locking on an rdm makes it safe to use a shared raw lun without losing data when two virtual machines on different servers try to access the same lun. Right now we have two file share luns 2tb and 5tb, that will be cleaned up and converted into a new sharepoint infrastructure that we are implementing.
Before that we need to convert the physical rdm to a virtual rdm. Veeam backup error, possibly mapped raw lun related. For details about rdm, see the vsphere storage documentation. Raw device mapping or rdm involves more configuration and ongoing operational overhead compared to vmfs. The rdm contains metadata for managing and redirecting disk access to the physical device. Done this for some very low downtime migrations of dbs and file servers with a ton of data. Makes it possible to use vmfs distributed locking for raw scsi devices. Older vmware documentation indicates rdm is not supported by locallyattached devices, which is no longer the case. In my previous article i shown adding and sharing rdm disk to multiple vms in vmware step by step, i received one related task to convert virtual machine rdm raw device mapping hard disk to vmdk disk. This just a file, which contains information about raw lun and it is locked by virtual center so that vm can write to lun. How to create vmware rdm physical compatibility disk. This mapping file, which has a vmdk extension, points to the raw device rdm file lock is translated to scsi reservation on the lun utilities like admsnap and admhost, installed on the virtual machines, can directly access the raw devicepartition. A physical connected rdm cannot be converted online to a vmdk.
You can carve that up into as many zfs filesystems as youd like. As we already discussed many times, vmware rdm raw device mapping is a mapping file that provides direct access to a lun on the fiber channel storage system for a virtual machine. Jan 22, 2018 vmware rdm raw device mapping is a mapping file that provides direct access to a lun on an iscsi or fibre channel storage system for a virtual machine. When you map a lun to vmfs, it creates a file with extension vmdk, which points to raw lun. Well, apparently, this case is not unique, so i decided to share my experience in todays. Mapping of the lun to esxi hosts is done as per normal. These vmdks can be added to your virtual machine using the vsphere client in the normal way just tell it that they are existing virtual disks and it works out the rest. Start adding lun as a vrdm, stop right before you hit apply. Each drive can be either a virtual disk or a raw device mapping. I found an article that states we can convert a vmdk file into a raw mapped drive, and this is the process we are looking to follow. The file gives you some of the advantages of direct access to a physical device while keeping some advantages of a virtual disk in vmfs. Cleaning up the mapped rdm luns in the guest operating system.
Rdms can be described in terms such as mapping a raw device into a datastore, mapping a system lun, or mapping a disk file to a physical disk. That includes zvols volumes that can be exported as block devices a major point of using zfs is to give you maximum storage flexibility for example, i have the following set of zfs filesystems, where the first four listed are nfs mounts exported. Creatingadding a raw device mapping rdm to a virtual. Convert a virtual disk vmdk in a physical disk and vice versa. Solved convert raw disk to vmdk virtualization spiceworks.
Run fewer servers and reduce capital and operating costs using vmware vsphere to build a cloud computing infrastructure. One of those 5 disks is mapped via esxi iscsi initiator and has the same capacity as osmounted iscsi volume, so at first sight i thought it is the same iscsi volume, somehow seen by converter. You will find the entire rdm mapped entry as mapped raw lun for every rdm entry. Vmware raw device mapping and file recovery diskinternals. Solved iscsi lun which is mounted from within the vm.
Creatingadding a raw device mapping rdm to a virtual machine. Removing a raw mapped lun from a vmware vm solutions. To give you some context, lets assume you receive a request to increase the k. This mapping file, which has a vmdk extension, points to the raw device rdm file lock is translated to scsi reservation on the lun utilities like admsnap and admhost, installed on the virtual machines, can directly access the. Pass through disk recommendations for vmware hyperconverged. Also, with direct access, physicaltovirtual conversion becomes possible without migrating a massive lun to vmdk. Storage admins used to match luns to physical servers, but thats all changed.
There is a misunderstanding that rdms offer greater performance compared to vmdk s on. The trick here is to put the rdm in virtual mode and use storage vmotion to migrate it to another lun. You can also use a storage vmotion operation to perform the same migration task. It is not possible to storagevmotion the iscsi disks without doing some work first see below as the hypervisor does not see continue reading converting iscsi targets in windows to vmdk. I logged into the windows virtual machine, configured the newlyadded storage, formatted the volume with ntfs and made it the r. How to convert rdm disk raw device mapping to vmdk. After that, bypassing the mapping file, reading, and writing goes directly to the lun. Actually, it was my mistake reading the converter output. Powercli script to identify which vm is using an rdm lun identified by the naaid of the lun. A virtual rdm behaves the same as a vmdk file based disk except that it is backed by raw block storage. When you open the lun for virtual machine access, the mapping file is read and thus receives a link to the raw lun. It seems the debate between using a vmdk on vmfs or an rdm still rages when it comes to the question which one is better for performance. I would like to remove this raw lun from the server and make it available to the sans for creating a new virtual disk.
Basically i require it to convert because, i was not going to use microsoft clustering anymore, also i was planning to change backend storage due to end of life. However, we can see hard disk 2 is mapped to a physical lun at the bottom of the screen shot you will not see that with a regular vmdk file. 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. It will list them as mapped raw lun in the vm configuration. With rdm, vmdk files are only pointers to a vms disk data, while on vmfs the files also hold. Rescan your hbas and check under storage adapters to ensure the cluster can see the lun. As we discussed in the earlier post, there are two types of rdm disks virtual compatibility rdm and physical compatibility rdm. Jan 12, 2014 mapping windows drives to rdms in vmware esxesxi january 12, 2014 by japinator it can be confusing when trying to identify the rdm that correlates to a windows drive.
Vmfs virtual file based disk vmdk or a raw device mapping rdm. The rdm allows a virtual machine to directly access and use the storage device. Convert iscsi mapped disk to vmware vmdk solutions experts. We have a sas box with 24 drives connected to openindiana server configured as a pool of 11 mirrored drives with two spares. High availability ha and drs in esx vmware vmfs vs rdm raw device mapping posted by craig on august 22nd, 2008 in virtualization 3 comments. Easily convert netapp luns to vhdx or vmdk files its magic. Jul 17, 2015 recently i was tasked with converting iscsi connected disks on windows servers to a new san. If the source vmdk is hosted on a lun, it must be an ntfs formatted lun mounted to the host running this commandlet. Some vsphere administrators utilize a storage feature called raw device mapping or rdm. Encapsulating disk information in a file allows vcenter server to lock the lun so that only one virtual machine can write to it at a time.