RDM disk

[BBP]

Hello Experts,

I want to add a new RDM disk to my VM.  When I tried to add a new RDM device,  LUN not showing.  So I thought, need to create a new software iSCSi adapter first in order to set up and RDM disk. So I tried to create a new software iSCSI adapter if one of my ESxi host, but the add iSCSI adapter option is greyed out. Please let me know how to setup a RDM disk to the VM. Please find the attached images for your reference.

Lab setup

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Host1- VMware ESxi 7.0.3

Host2- VMware ESxi 7.0.3

Host3- VMware ESxi 7.0.3

VCSA 7

 

[Scott Vessey]

Need more info about the LUN you want to use, is it new, was it existing, is it seen correctly by the hosts, does it contain a VMFS?

 

[BBP]

  Thank you for your quick response. It is existing iscsi datastore Capacity 39 GB. From this 39 GB I want to assign 5 GB  disk space to my VM RDM disk. Please find the screenshots for your reference.

[Scott Vessey]

You can’t do that using an RDM as the LUN already contains a VMFS datastore.

You could create a 5GB virtual disk (VMDK) for the VM if the datastore has enough free space.

[BBP]

  Thank You for your response.

[BBP]

  I have created a new 5 GB virtual disk for the VM. When i am trying assign 5 GB disk space to the VM, by adding a RDM disk there is no LUN showing. Please find the attached screenshots for your reference.

[Scott Vessey]

I meant to create a virtual hard disk at the VM level, placing the VMDK files in an existing datastore.

Why do you actually want to use an RDM?

You can’t use a LUN as a VMFS datastore and as a target for an RDM - it is either/or.

 

[BBP]

  Yes I want to create a virtual hard disk at the VM level only. I think you are not getting my point. I am attaching screenshots hope you will get the exact issue what i am facing. In my windows 2012 R2 server my C drive has 30 GB capacity. from this 39 GB, i want to assign 5 GB  storage space to the RDM disk which will directly map to my another windows VM.  The drive showing as connected in windows server iscsi file and storage services section. But when i am trying to add new RDM disk i am not getting this 5 GB disk space.

[BBP]

  Why i want to create a RDM  disk ,only for testing purpose to check if snapshot is happening or not.

[Scott Vessey]

Nope, I clearly misunderstand what you're trying to do.

Hopefully someone else will understand and be able to help you.

 

[Duncan Epping]

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 wrote:

  Thank you for your quick response. It is existing iscsi datastore Capacity 39 GB. From this 39 GB I want to assign 5 GB  disk space to my VM RDM disk. Please find the screenshots for your reference.

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That is not how an RDM works. "RDM" stands for Raw Device Mapping. If you have a 39GB device presented, your RDM will be 39GB as you are passing the FULL device directly to the VM! You cannot allocate a portion. Also, the volume CANNOT contain a VMFS file system, in other words, it should be a new volume.

If you simply want to add a 5GB disk to a VM, you need to add a new virtual disk, not an RDM. This disk will then be stored as a file on that VMFS iSCSI datastore.

[BBP]

Yes you are right RDM" stands for Raw Device Mapping. What my understanding is suppose we have 1 TB storage space and we want to assign 500 GB  direct to your VM then RDM comes to picture. Any way the issue is resolved. I have attached the screenshot where i assigned 5 GB storage space to my new VM from 39 GB disk space. My windows 2012 R2 server acts as a iSCSI target and ESxi hosts are iSCSi initiator

I created a new VM inside ESxi host..then assigned 5 GB RDM disk direct to this VM. 

[Duncan Epping]

Nah, RDMs are used for very specific use cases. Not specifically for particular sizes. We have customers with VMFS Datastores which are 30TB large (or bigger even) and VMs with multiple TBs of regular VMDKs.

No idea how you create an RDM volume from a VMFS Datastore, but anyway, problem solved.

[BBP]

  I have not created an RDM volume from a VMFS Datastore.  I have a windows 2012R2 sever and it has 40 GB disk space assigned to c drive. From this 40 GB i have assigned 5 GB to the new VM . You can see the image which i have attached. The file format is NTFS not VMFS

[RajeevVCP4]

When you are trying to add RDM what option you are getting on VM

You can try this

 

https://kb.vmware.com/s/article/1017530

 

 

[BBP]

  when I am trying to add   RDM , I am not getting any LUN to add. Now i am facing another issue. My iscsi datastore are not showing . When I am trying to connect the ESxi host direct using host client i am getting an error.

 

 

[BBP]

  Any idea why iSCSI-Datastore is not showing .iscsi volumes that are showing as mounted under the iscsi hba but it is not showing up as a datastore .