RDM Allocation and local mapping file size

[VMW_Gather_Help]

I am wanting to use a Direct LUN attachment from my SAN using RDM passthrough to a VM for my VEEAM BU Storage Volumes. These are two storage volumes, both greater than 6TB each. This would allow me to do hardware level snapshots on the SAN.

When I allocated a new RDM disk to the VM and choose the LUN, it appears to create .vmdk descriptor files and rdmp.vmdk mapping files in the VM datastore with the VM files. I am not clear if these rdmp.vmdk files are duplicates of the data in the LUN allocation or if these are the data files being stored in the wrong place?

Is this working as designed? If so are these rdmp.vmdk files really the same size as the LUN data? Do I really need 13 TB of local datastore space allocated to represent the data mapping for 13 TB of SAN LUN data? This seems to be double allocation of the space? Am I missing something in this concept?

[scott28tt · Accepted solution]

No, the vmdk files associated with an RDM do not store a copy of all the data of the LUN.

[a_p_ · Accepted solution]

In addition to what Scott said, the size that you see shows the provisioned size, i.e. not the consumed disk space for these .vmdk pointer files.

If you want, run ls -lisa *.vmdk in the VM's folder, which will show you the consumed disk space on the datastore in kB in the second column.

André

[VMW_Gather_Help · Accepted solution]

Thanks you both for the confirmation on how this works.

Best regards